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 $140.99   11.761%   $157.5718   $157.57   $157.55   $157.60  
  Purchase #2 $174.99   10.252%   $192.93   $192.93   $192.95   $192.90  
  Purchase #3 $249.26   7.720%   $268.5029   $268.50   $268.50   $268.50  
  Purchase #4 $83.46   11.288%   $92.881   $92.88   $92.90   $92.90  
  Purchase #5 $160.56   13.357%   $182.006   $182.01   $182.00   $182.00  
  Purchase #6 $56.95   13.393%   $64.5773   $64.58   $64.60   $64.60  
  Purchase #7 $227.65   7.295%   $244.2571   $244.26   $244.25   $244.30  
  7 purchase totals = $1,093.86       $1,202.7261   $1,202.73   $1,202.75   $1,202.80