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 $177.56   11.244%   $197.5248   $197.52   $197.50   $197.50  
  Purchase #2 $52.84   8.561%   $57.3636   $57.36   $57.35   $57.40  
  Purchase #3 $195.83   7.675%   $210.86   $210.86   $210.85   $210.90  
  Purchase #4 $25.36   5.323%   $26.7099   $26.71   $26.70   $26.70  
  Purchase #5 $163.66   4.122%   $170.4061   $170.41   $170.40   $170.40  
  Purchase #6 $217.49   9.341%   $237.8057   $237.81   $237.80   $237.80  
  Purchase #7 $51.76   7.410%   $55.5954   $55.60   $55.60   $55.60  
  7 purchase totals = $884.50       $956.2655   $956.27   $956.20   $956.30