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 $86.98   12.184%   $97.5776   $97.58   $97.60   $97.60  
  Purchase #2 $93.87   6.127%   $99.6214   $99.62   $99.60   $99.60  
  Purchase #3 $248.66   7.241%   $266.6655   $266.67   $266.65   $266.70  
  Purchase #4 $199.80   7.290%   $214.3654   $214.37   $214.35   $214.40  
  Purchase #5 $42.43   6.341%   $45.1205   $45.12   $45.10   $45.10  
  Purchase #6 $210.60   8.755%   $229.038   $229.04   $229.05   $229.00  
  Purchase #7 $43.27   13.298%   $49.024   $49.02   $49.00   $49.00  
  7 purchase totals = $925.61       $1,001.4124   $1,001.42   $1,001.35   $1,001.40