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 $182.89   6.102%   $194.0499   $194.05   $194.05   $194.00  
  Purchase #2 $93.45   4.802%   $97.9375   $97.94   $97.95   $97.90  
  Purchase #3 $207.57   11.416%   $231.2662   $231.27   $231.25   $231.30  
  Purchase #4 $147.56   11.522%   $164.5619   $164.56   $164.55   $164.60  
  Purchase #5 $53.69   9.602%   $58.8453   $58.85   $58.85   $58.80  
  Purchase #6 $8.80   10.152%   $9.6934   $9.69   $9.70   $9.70  
  Purchase #7 $39.84   5.155%   $41.8938   $41.89   $41.90   $41.90  
  7 purchase totals = $733.80       $798.2480   $798.25   $798.25   $798.20