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 $69.89   8.294%   $75.6867   $75.69   $75.70   $75.70  
  Purchase #2 $146.78   7.638%   $157.9911   $157.99   $158.00   $158.00  
  Purchase #3 $60.25   11.739%   $67.3227   $67.32   $67.30   $67.30  
  Purchase #4 $35.25   3.354%   $36.4323   $36.43   $36.45   $36.40  
  Purchase #5 $134.57   6.322%   $143.0775   $143.08   $143.10   $143.10  
  Purchase #6 $216.33   13.736%   $246.0451   $246.05   $246.05   $246.00  
  Purchase #7 $87.69   5.468%   $92.4849   $92.48   $92.50   $92.50  
  7 purchase totals = $750.76       $819.0403   $819.04   $819.10   $819.00