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 $208.56   11.221%   $231.9625   $231.96   $231.95   $232.00  
  Purchase #2 $54.50   13.266%   $61.73   $61.73   $61.75   $61.70  
  Purchase #3 $195.49   10.560%   $216.1337   $216.13   $216.15   $216.10  
  Purchase #4 $27.70   9.370%   $30.2955   $30.30   $30.30   $30.30  
  Purchase #5 $169.75   3.576%   $175.8203   $175.82   $175.80   $175.80  
  Purchase #6 $34.96   4.551%   $36.551   $36.55   $36.55   $36.60  
  Purchase #7 $166.66   4.582%   $174.2964   $174.30   $174.30   $174.30  
  7 purchase totals = $857.62       $926.7894   $926.79   $926.80   $926.80