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 $209.39   3.161%   $216.0088   $216.01   $216.00   $216.00  
  Purchase #2 $157.47   10.294%   $173.68   $173.68   $173.70   $173.70  
  Purchase #3 $233.42   8.147%   $252.4367   $252.44   $252.45   $252.40  
  Purchase #4 $19.94   5.607%   $21.058   $21.06   $21.05   $21.10  
  Purchase #5 $62.53   13.452%   $70.9415   $70.94   $70.95   $70.90  
  Purchase #6 $8.74   7.211%   $9.3702   $9.37   $9.35   $9.40  
  Purchase #7 $211.70   6.508%   $225.4774   $225.48   $225.50   $225.50  
  7 purchase totals = $903.19       $968.9726   $968.98   $969.00   $969.00