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 $108.71   8.363%   $117.8014   $117.80   $117.80   $117.80  
  Purchase #2 $59.32   12.371%   $66.6585   $66.66   $66.65   $66.70  
  Purchase #3 $70.53   3.657%   $73.1093   $73.11   $73.10   $73.10  
  Purchase #4 $238.61   6.753%   $254.7233   $254.72   $254.70   $254.70  
  Purchase #5 $28.69   6.383%   $30.5213   $30.52   $30.50   $30.50  
  Purchase #6 $19.44   9.153%   $21.2193   $21.22   $21.20   $21.20  
  Purchase #7 $246.40   3.482%   $254.9796   $254.98   $255.00   $255.00  
  7 purchase totals = $771.70       $819.0127   $819.01   $818.95   $819.00