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 $62.57   5.198%   $65.8224   $65.82   $65.80   $65.80  
  Purchase #2 $98.69   13.838%   $112.3467   $112.35   $112.35   $112.30  
  Purchase #3 $232.40   7.826%   $250.5876   $250.59   $250.60   $250.60  
  Purchase #4 $220.73   13.477%   $250.4778   $250.48   $250.50   $250.50  
  Purchase #5 $153.79   10.777%   $170.3639   $170.36   $170.35   $170.40  
  Purchase #6 $63.73   6.277%   $67.7303   $67.73   $67.75   $67.70  
  Purchase #7 $44.51   13.743%   $50.627   $50.63   $50.65   $50.60  
  7 purchase totals = $876.42       $967.9557   $967.96   $968.00   $967.90