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 $208.34   3.658%   $215.9611   $215.96   $215.95   $216.00  
  Purchase #2 $159.42   4.838%   $167.1327   $167.13   $167.15   $167.10  
  Purchase #3 $204.71   6.456%   $217.9261   $217.93   $217.95   $217.90  
  Purchase #4 $239.77   11.452%   $267.2285   $267.23   $267.25   $267.20  
  Purchase #5 $224.75   4.874%   $235.7043   $235.70   $235.70   $235.70  
  Purchase #6 $36.83   11.864%   $41.1995   $41.20   $41.20   $41.20  
  Purchase #7 $7.54   8.158%   $8.1551   $8.16   $8.15   $8.20  
  7 purchase totals = $1,081.36       $1,153.3073   $1,153.31   $1,153.35   $1,153.30