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 $69.97   7.244%   $75.0386   $75.04   $75.05   $75.00  
  Purchase #2 $122.37   11.131%   $135.991   $135.99   $136.00   $136.00  
  Purchase #3 $198.70   12.373%   $223.2852   $223.29   $223.30   $223.30  
  Purchase #4 $175.67   6.713%   $187.4627   $187.46   $187.45   $187.50  
  Purchase #5 $56.39   9.868%   $61.9546   $61.95   $61.95   $62.00  
  Purchase #6 $56.67   3.853%   $58.8535   $58.85   $58.85   $58.90  
  Purchase #7 $149.89   11.155%   $166.6102   $166.61   $166.60   $166.60  
  7 purchase totals = $829.66       $909.1958   $909.19   $909.20   $909.30