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 $217.25   13.679%   $246.9676   $246.97   $246.95   $247.00  
  Purchase #2 $141.54   13.169%   $160.1794   $160.18   $160.20   $160.20  
  Purchase #3 $114.55   13.154%   $129.6179   $129.62   $129.60   $129.60  
  Purchase #4 $239.69   9.408%   $262.24   $262.24   $262.25   $262.20  
  Purchase #5 $196.88   3.442%   $203.6566   $203.66   $203.65   $203.70  
  Purchase #6 $146.53   11.747%   $163.7429   $163.74   $163.75   $163.70  
  Purchase #7 $221.63   10.349%   $244.5665   $244.57   $244.55   $244.60  
  7 purchase totals = $1,278.07       $1,410.9709   $1,410.98   $1,410.95   $1,411.00