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 $196.68   10.247%   $216.8338   $216.83   $216.85   $216.80  
  Purchase #2 $58.76   6.730%   $62.7145   $62.71   $62.70   $62.70  
  Purchase #3 $82.71   13.445%   $93.8304   $93.83   $93.85   $93.80  
  Purchase #4 $43.65   5.301%   $45.9639   $45.96   $45.95   $46.00  
  Purchase #5 $170.53   8.162%   $184.4487   $184.45   $184.45   $184.40  
  Purchase #6 $61.66   11.118%   $68.5154   $68.52   $68.50   $68.50  
  Purchase #7 $75.80   8.388%   $82.1581   $82.16   $82.15   $82.20  
  7 purchase totals = $689.79       $754.4648   $754.46   $754.45   $754.40