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 $112.44   8.255%   $121.7219   $121.72   $121.70   $121.70  
  Purchase #2 $194.63   4.539%   $203.4643   $203.46   $203.45   $203.50  
  Purchase #3 $89.49   7.140%   $95.8796   $95.88   $95.90   $95.90  
  Purchase #4 $244.44   8.183%   $264.4425   $264.44   $264.45   $264.40  
  Purchase #5 $69.31   5.721%   $73.2752   $73.28   $73.30   $73.30  
  Purchase #6 $227.75   4.215%   $237.3497   $237.35   $237.35   $237.30  
  Purchase #7 $55.60   6.372%   $59.1428   $59.14   $59.15   $59.10  
  7 purchase totals = $993.66       $1,055.2760   $1,055.27   $1,055.30   $1,055.20