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 $223.83   6.534%   $238.4551   $238.46   $238.45   $238.50  
  Purchase #2 $234.47   10.720%   $259.6052   $259.61   $259.60   $259.60  
  Purchase #3 $23.35   7.232%   $25.0387   $25.04   $25.05   $25.00  
  Purchase #4 $150.36   12.448%   $169.0768   $169.08   $169.10   $169.10  
  Purchase #5 $167.54   5.517%   $176.7832   $176.78   $176.80   $176.80  
  Purchase #6 $223.29   9.240%   $243.922   $243.92   $243.90   $243.90  
  Purchase #7 $57.98   7.497%   $62.3268   $62.33   $62.35   $62.30  
  7 purchase totals = $1,080.82       $1,175.2078   $1,175.22   $1,175.25   $1,175.20