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 $83.76   12.186%   $93.967   $93.97   $93.95   $94.00  
  Purchase #2 $22.70   9.745%   $24.9121   $24.91   $24.90   $24.90  
  Purchase #3 $196.98   11.274%   $219.1875   $219.19   $219.20   $219.20  
  Purchase #4 $45.34   12.312%   $50.9223   $50.92   $50.90   $50.90  
  Purchase #5 $217.86   11.549%   $243.0207   $243.02   $243.00   $243.00  
  Purchase #6 $92.60   10.712%   $102.5193   $102.52   $102.50   $102.50  
  Purchase #7 $20.74   8.514%   $22.5058   $22.51   $22.50   $22.50  
  7 purchase totals = $679.98       $757.0347   $757.04   $756.95   $757.00