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 $36.32   13.290%   $41.1469   $41.15   $41.15   $41.10  
  Purchase #2 $160.76   5.221%   $169.1533   $169.15   $169.15   $169.20  
  Purchase #3 $29.44   4.367%   $30.7256   $30.73   $30.75   $30.70  
  Purchase #4 $217.49   6.221%   $231.0201   $231.02   $231.00   $231.00  
  Purchase #5 $182.56   11.600%   $203.737   $203.74   $203.75   $203.70  
  Purchase #6 $84.25   6.231%   $89.4996   $89.50   $89.50   $89.50  
  Purchase #7 $155.28   8.546%   $168.5502   $168.55   $168.55   $168.60  
  7 purchase totals = $866.10       $933.8327   $933.84   $933.85   $933.80