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 $244.85   7.801%   $263.9507   $263.95   $263.95   $264.00  
  Purchase #2 $199.96   6.246%   $212.4495   $212.45   $212.45   $212.40  
  Purchase #3 $91.69   13.218%   $103.8096   $103.81   $103.80   $103.80  
  Purchase #4 $219.78   8.859%   $239.2503   $239.25   $239.25   $239.30  
  Purchase #5 $222.52   7.595%   $239.4204   $239.42   $239.40   $239.40  
  Purchase #6 $238.78   10.676%   $264.2722   $264.27   $264.25   $264.30  
  Purchase #7 $54.34   10.771%   $60.193   $60.19   $60.20   $60.20  
  7 purchase totals = $1,271.92       $1,383.3457   $1,383.34   $1,383.30   $1,383.40