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 $49.27   13.555%   $55.9485   $55.95   $55.95   $55.90  
  Purchase #2 $202.47   4.343%   $211.2633   $211.26   $211.25   $211.30  
  Purchase #3 $248.31   10.824%   $275.1871   $275.19   $275.20   $275.20  
  Purchase #4 $31.36   13.187%   $35.4954   $35.50   $35.50   $35.50  
  Purchase #5 $199.30   8.278%   $215.7981   $215.80   $215.80   $215.80  
  Purchase #6 $150.53   7.617%   $161.9959   $162.00   $162.00   $162.00  
  Purchase #7 $181.89   11.836%   $203.4185   $203.42   $203.40   $203.40  
  7 purchase totals = $1,063.13       $1,159.1068   $1,159.12   $1,159.10   $1,159.10