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 $217.31   13.578%   $246.8164   $246.82   $246.80   $246.80  
  Purchase #2 $134.31   8.694%   $145.9869   $145.99   $146.00   $146.00  
  Purchase #3 $117.58   5.793%   $124.3914   $124.39   $124.40   $124.40  
  Purchase #4 $152.52   4.529%   $159.4276   $159.43   $159.45   $159.40  
  Purchase #5 $128.30   9.173%   $140.069   $140.07   $140.05   $140.10  
  Purchase #6 $159.59   12.138%   $178.961   $178.96   $178.95   $179.00  
  Purchase #7 $211.39   11.804%   $236.3425   $236.34   $236.35   $236.30  
  7 purchase totals = $1,121.00       $1,231.9948   $1,232.00   $1,232.00   $1,232.00