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 $98.50   6.170%   $104.5775   $104.58   $104.60   $104.60  
  Purchase #2 $219.94   13.826%   $250.3489   $250.35   $250.35   $250.30  
  Purchase #3 $205.63   5.485%   $216.9088   $216.91   $216.90   $216.90  
  Purchase #4 $160.99   13.282%   $182.3727   $182.37   $182.35   $182.40  
  Purchase #5 $44.58   6.137%   $47.3159   $47.32   $47.30   $47.30  
  Purchase #6 $138.81   13.668%   $157.7826   $157.78   $157.80   $157.80  
  Purchase #7 $49.88   10.166%   $54.9508   $54.95   $54.95   $55.00  
  7 purchase totals = $918.33       $1,014.2572   $1,014.26   $1,014.25   $1,014.30