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 $52.67   12.110%   $59.0483   $59.05   $59.05   $59.00  
  Purchase #2 $208.88   11.125%   $232.1179   $232.12   $232.10   $232.10  
  Purchase #3 $29.27   11.265%   $32.5673   $32.57   $32.55   $32.60  
  Purchase #4 $67.62   13.441%   $76.7088   $76.71   $76.70   $76.70  
  Purchase #5 $29.26   12.588%   $32.9432   $32.94   $32.95   $32.90  
  Purchase #6 $184.93   12.715%   $208.4438   $208.44   $208.45   $208.40  
  Purchase #7 $6.70   11.693%   $7.4834   $7.48   $7.50   $7.50  
  7 purchase totals = $579.33       $649.3127   $649.31   $649.30   $649.20