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 $42.66   9.657%   $46.7797   $46.78   $46.80   $46.80  
  Purchase #2 $92.35   12.556%   $103.9455   $103.95   $103.95   $103.90  
  Purchase #3 $14.80   9.309%   $16.1777   $16.18   $16.20   $16.20  
  Purchase #4 $68.78   10.419%   $75.9462   $75.95   $75.95   $75.90  
  Purchase #5 $72.74   11.182%   $80.8738   $80.87   $80.85   $80.90  
  Purchase #6 $234.77   6.366%   $249.7155   $249.72   $249.70   $249.70  
  Purchase #7 $153.67   8.687%   $167.0193   $167.02   $167.00   $167.00  
  7 purchase totals = $679.77       $740.4577   $740.47   $740.45   $740.40