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 $212.35   11.193%   $236.1183   $236.12   $236.10   $236.10  
  Purchase #2 $118.85   13.817%   $135.2715   $135.27   $135.25   $135.30  
  Purchase #3 $176.90   6.293%   $188.0323   $188.03   $188.05   $188.00  
  Purchase #4 $205.25   13.262%   $232.4703   $232.47   $232.45   $232.50  
  Purchase #5 $124.78   7.853%   $134.579   $134.58   $134.60   $134.60  
  Purchase #6 $241.48   10.595%   $267.0648   $267.06   $267.05   $267.10  
  Purchase #7 $8.62   4.676%   $9.0231   $9.02   $9.00   $9.00  
  7 purchase totals = $1,088.23       $1,202.5593   $1,202.55   $1,202.50   $1,202.60