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 $233.63   8.730%   $254.0259   $254.03   $254.05   $254.00  
  Purchase #2 $229.36   9.439%   $251.0093   $251.01   $251.00   $251.00  
  Purchase #3 $199.75   8.674%   $217.0763   $217.08   $217.10   $217.10  
  Purchase #4 $223.54   7.628%   $240.5916   $240.59   $240.60   $240.60  
  Purchase #5 $202.26   9.371%   $221.2138   $221.21   $221.20   $221.20  
  Purchase #6 $157.45   7.642%   $169.4823   $169.48   $169.50   $169.50  
  Purchase #7 $203.76   12.466%   $229.1607   $229.16   $229.15   $229.20  
  7 purchase totals = $1,449.75       $1,582.5599   $1,582.56   $1,582.60   $1,582.60