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 $229.93   13.408%   $260.759   $260.76   $260.75   $260.80  
  Purchase #2 $194.51   12.822%   $219.4501   $219.45   $219.45   $219.50  
  Purchase #3 $107.63   8.557%   $116.8399   $116.84   $116.85   $116.80  
  Purchase #4 $22.73   8.447%   $24.65   $24.65   $24.65   $24.70  
  Purchase #5 $103.28   5.714%   $109.1814   $109.18   $109.20   $109.20  
  Purchase #6 $78.98   4.504%   $82.5373   $82.54   $82.55   $82.50  
  Purchase #7 $126.65   13.258%   $143.4413   $143.44   $143.45   $143.40  
  7 purchase totals = $863.71       $956.8590   $956.86   $956.90   $956.90