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 $208.85   10.606%   $231.0006   $231.00   $231.00   $231.00  
  Purchase #2 $232.57   3.819%   $241.4518   $241.45   $241.45   $241.50  
  Purchase #3 $58.42   9.661%   $64.064   $64.06   $64.05   $64.10  
  Purchase #4 $21.68   6.268%   $23.0389   $23.04   $23.05   $23.00  
  Purchase #5 $20.67   5.263%   $21.7579   $21.76   $21.75   $21.80  
  Purchase #6 $140.73   11.310%   $156.6466   $156.65   $156.65   $156.60  
  Purchase #7 $76.65   9.833%   $84.187   $84.19   $84.20   $84.20  
  7 purchase totals = $759.57       $822.1468   $822.15   $822.15   $822.20