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 $210.65   10.248%   $232.2374   $232.24   $232.25   $232.20  
  Purchase #2 $61.67   3.353%   $63.7378   $63.74   $63.75   $63.70  
  Purchase #3 $162.51   5.399%   $171.2839   $171.28   $171.30   $171.30  
  Purchase #4 $184.65   12.167%   $207.1164   $207.12   $207.10   $207.10  
  Purchase #5 $59.30   5.117%   $62.3344   $62.33   $62.35   $62.30  
  Purchase #6 $7.63   12.857%   $8.611   $8.61   $8.60   $8.60  
  Purchase #7 $190.97   5.594%   $201.6529   $201.65   $201.65   $201.70  
  7 purchase totals = $877.38       $946.9738   $946.97   $947.00   $946.90