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 $232.72   6.532%   $247.9213   $247.92   $247.90   $247.90  
  Purchase #2 $104.77   12.294%   $117.6504   $117.65   $117.65   $117.70  
  Purchase #3 $19.37   12.609%   $21.8124   $21.81   $21.80   $21.80  
  Purchase #4 $36.28   12.617%   $40.8574   $40.86   $40.85   $40.90  
  Purchase #5 $204.53   6.738%   $218.3112   $218.31   $218.30   $218.30  
  Purchase #6 $92.81   10.140%   $102.2209   $102.22   $102.20   $102.20  
  Purchase #7 $116.60   6.605%   $124.3014   $124.30   $124.30   $124.30  
  7 purchase totals = $807.08       $873.0750   $873.07   $873.00   $873.10