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 $54.33   8.688%   $59.0502   $59.05   $59.05   $59.10  
  Purchase #2 $143.36   12.389%   $161.1209   $161.12   $161.10   $161.10  
  Purchase #3 $250.30   7.288%   $268.5419   $268.54   $268.55   $268.50  
  Purchase #4 $223.85   5.582%   $236.3453   $236.35   $236.35   $236.30  
  Purchase #5 $236.30   5.785%   $249.97   $249.97   $249.95   $250.00  
  Purchase #6 $194.63   7.394%   $209.0209   $209.02   $209.00   $209.00  
  Purchase #7 $155.72   7.415%   $167.2666   $167.27   $167.25   $167.30  
  7 purchase totals = $1,258.49       $1,351.3158   $1,351.32   $1,351.25   $1,351.30