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 $183.70   8.201%   $198.7652   $198.77   $198.75   $198.80  
  Purchase #2 $10.29   12.785%   $11.6056   $11.61   $11.60   $11.60  
  Purchase #3 $171.87   8.867%   $187.1097   $187.11   $187.10   $187.10  
  Purchase #4 $113.47   7.455%   $121.9292   $121.93   $121.95   $121.90  
  Purchase #5 $72.53   4.275%   $75.6307   $75.63   $75.65   $75.60  
  Purchase #6 $235.86   4.388%   $246.2095   $246.21   $246.20   $246.20  
  Purchase #7 $19.96   11.250%   $22.2055   $22.21   $22.20   $22.20  
  7 purchase totals = $807.68       $863.4554   $863.47   $863.45   $863.40