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 $240.61   8.137%   $260.1884   $260.19   $260.20   $260.20  
  Purchase #2 $194.62   6.285%   $206.8519   $206.85   $206.85   $206.90  
  Purchase #3 $228.56   6.725%   $243.9307   $243.93   $243.95   $243.90  
  Purchase #4 $16.98   3.252%   $17.5322   $17.53   $17.55   $17.50  
  Purchase #5 $114.76   13.415%   $130.1551   $130.16   $130.15   $130.20  
  Purchase #6 $41.85   5.815%   $44.2836   $44.28   $44.30   $44.30  
  Purchase #7 $220.86   10.871%   $244.8697   $244.87   $244.85   $244.90  
  7 purchase totals = $1,058.24       $1,147.8116   $1,147.81   $1,147.85   $1,147.90