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 $58.95   12.533%   $66.3382   $66.34   $66.35   $66.30  
  Purchase #2 $241.77   13.461%   $274.3147   $274.31   $274.30   $274.30  
  Purchase #3 $231.29   8.614%   $251.2133   $251.21   $251.20   $251.20  
  Purchase #4 $41.65   13.105%   $47.1082   $47.11   $47.10   $47.10  
  Purchase #5 $156.59   4.639%   $163.8542   $163.85   $163.85   $163.90  
  Purchase #6 $59.33   3.406%   $61.3508   $61.35   $61.35   $61.40  
  Purchase #7 $98.62   6.301%   $104.834   $104.83   $104.85   $104.80  
  7 purchase totals = $888.20       $969.0134   $969.00   $969.00   $969.00