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 $61.26   13.321%   $69.4204   $69.42   $69.40   $69.40  
  Purchase #2 $230.48   13.220%   $260.9495   $260.95   $260.95   $260.90  
  Purchase #3 $247.28   7.151%   $264.963   $264.96   $264.95   $265.00  
  Purchase #4 $60.79   3.305%   $62.7991   $62.80   $62.80   $62.80  
  Purchase #5 $230.67   6.364%   $245.3498   $245.35   $245.35   $245.30  
  Purchase #6 $239.61   8.827%   $260.7604   $260.76   $260.75   $260.80  
  Purchase #7 $141.48   12.220%   $158.7689   $158.77   $158.75   $158.80  
  7 purchase totals = $1,211.57       $1,323.0111   $1,323.01   $1,322.95   $1,323.00