Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $191.53   9.121%   $208.9995   $209.00   $209.00   $209.00  
  Purchase #2 $237.46   12.249%   $266.5465   $266.55   $266.55   $266.50  
  Purchase #3 $216.41   11.439%   $241.1651   $241.17   $241.15   $241.20  
  Purchase #4 $170.72   5.241%   $179.6674   $179.67   $179.65   $179.70  
  Purchase #5 $225.95   12.378%   $253.9181   $253.92   $253.90   $253.90  
  Purchase #6 $224.60   7.171%   $240.7061   $240.71   $240.70   $240.70  
  Purchase #7 $112.61   10.253%   $124.1559   $124.16   $124.15   $124.20  
  7 purchase totals = $1,379.28       $1,515.1586   $1,515.18   $1,515.10   $1,515.20