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 $244.46   8.223%   $264.5619   $264.56   $264.55   $264.60  
  Purchase #2 $11.81   11.267%   $13.1406   $13.14   $13.15   $13.10  
  Purchase #3 $137.89   10.351%   $152.163   $152.16   $152.15   $152.20  
  Purchase #4 $154.39   5.464%   $162.8259   $162.83   $162.85   $162.80  
  Purchase #5 $40.88   9.341%   $44.6986   $44.70   $44.70   $44.70  
  Purchase #6 $246.36   6.608%   $262.6395   $262.64   $262.65   $262.60  
  Purchase #7 $149.54   6.784%   $159.6848   $159.68   $159.70   $159.70  
  7 purchase totals = $985.33       $1,059.7143   $1,059.71   $1,059.75   $1,059.70