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 $142.77   5.833%   $151.0978   $151.10   $151.10   $151.10  
  Purchase #2 $56.32   4.695%   $58.9642   $58.96   $58.95   $59.00  
  Purchase #3 $236.45   12.495%   $265.9944   $265.99   $266.00   $266.00  
  Purchase #4 $85.36   7.789%   $92.0087   $92.01   $92.00   $92.00  
  Purchase #5 $235.85   12.751%   $265.9232   $265.92   $265.90   $265.90  
  Purchase #6 $77.25   10.853%   $85.6339   $85.63   $85.65   $85.60  
  Purchase #7 $10.65   6.565%   $11.3492   $11.35   $11.35   $11.30  
  7 purchase totals = $844.65       $930.9714   $930.96   $930.95   $930.90