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 $237.50   12.645%   $267.5319   $267.53   $267.55   $267.50  
  Purchase #2 $108.52   11.253%   $120.7318   $120.73   $120.75   $120.70  
  Purchase #3 $119.51   5.686%   $126.3053   $126.31   $126.30   $126.30  
  Purchase #4 $219.90   11.304%   $244.7575   $244.76   $244.75   $244.80  
  Purchase #5 $198.51   12.807%   $223.9332   $223.93   $223.95   $223.90  
  Purchase #6 $14.44   10.218%   $15.9155   $15.92   $15.90   $15.90  
  Purchase #7 $208.39   12.335%   $234.0949   $234.09   $234.10   $234.10  
  7 purchase totals = $1,106.77       $1,233.2701   $1,233.27   $1,233.30   $1,233.20