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 $53.92   7.529%   $57.9796   $57.98   $58.00   $58.00  
  Purchase #2 $189.86   10.347%   $209.5048   $209.50   $209.50   $209.50  
  Purchase #3 $231.43   12.160%   $259.5719   $259.57   $259.55   $259.60  
  Purchase #4 $35.40   8.312%   $38.3424   $38.34   $38.35   $38.30  
  Purchase #5 $69.93   6.218%   $74.2782   $74.28   $74.30   $74.30  
  Purchase #6 $45.84   6.407%   $48.777   $48.78   $48.80   $48.80  
  Purchase #7 $102.86   13.749%   $117.0022   $117.00   $117.00   $117.00  
  7 purchase totals = $729.24       $805.4561   $805.45   $805.50   $805.50