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 $126.68   11.270%   $140.9568   $140.96   $140.95   $141.00  
  Purchase #2 $65.43   10.668%   $72.4101   $72.41   $72.40   $72.40  
  Purchase #3 $88.69   9.433%   $97.0561   $97.06   $97.05   $97.10  
  Purchase #4 $24.50   10.476%   $27.0666   $27.07   $27.05   $27.10  
  Purchase #5 $235.77   3.614%   $244.2907   $244.29   $244.30   $244.30  
  Purchase #6 $179.99   11.562%   $200.8004   $200.80   $200.80   $200.80  
  Purchase #7 $81.75   7.397%   $87.797   $87.80   $87.80   $87.80  
  7 purchase totals = $802.81       $870.3777   $870.39   $870.35   $870.50