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 $240.66   6.287%   $255.7903   $255.79   $255.80   $255.80  
  Purchase #2 $159.99   11.674%   $178.6672   $178.67   $178.65   $178.70  
  Purchase #3 $119.87   4.391%   $125.1335   $125.13   $125.15   $125.10  
  Purchase #4 $184.49   10.340%   $203.5663   $203.57   $203.55   $203.60  
  Purchase #5 $104.91   4.810%   $109.9562   $109.96   $109.95   $110.00  
  Purchase #6 $50.52   12.593%   $56.882   $56.88   $56.90   $56.90  
  Purchase #7 $131.90   5.341%   $138.9448   $138.94   $138.95   $138.90  
  7 purchase totals = $992.34       $1,068.9403   $1,068.94   $1,068.95   $1,069.00