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 $210.67   12.176%   $236.3212   $236.32   $236.30   $236.30  
  Purchase #2 $178.53   10.616%   $197.4827   $197.48   $197.50   $197.50  
  Purchase #3 $48.65   8.862%   $52.9614   $52.96   $52.95   $53.00  
  Purchase #4 $34.86   11.668%   $38.9275   $38.93   $38.95   $38.90  
  Purchase #5 $244.95   10.409%   $270.4468   $270.45   $270.45   $270.40  
  Purchase #6 $197.75   8.388%   $214.3373   $214.34   $214.35   $214.30  
  Purchase #7 $175.25   13.842%   $199.5081   $199.51   $199.50   $199.50  
  7 purchase totals = $1,090.66       $1,209.9850   $1,209.99   $1,210.00   $1,209.90