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 $203.47   10.676%   $225.1925   $225.19   $225.20   $225.20  
  Purchase #2 $160.99   6.504%   $171.4608   $171.46   $171.45   $171.50  
  Purchase #3 $112.96   9.682%   $123.8968   $123.90   $123.90   $123.90  
  Purchase #4 $158.44   10.704%   $175.3994   $175.40   $175.40   $175.40  
  Purchase #5 $85.79   13.679%   $97.5252   $97.53   $97.55   $97.50  
  Purchase #6 $119.93   12.225%   $134.5914   $134.59   $134.60   $134.60  
  Purchase #7 $64.84   3.181%   $66.9026   $66.90   $66.90   $66.90  
  7 purchase totals = $906.42       $994.9687   $994.97   $995.00   $995.00