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 $169.66   9.578%   $185.91   $185.91   $185.90   $185.90  
  Purchase #2 $236.58   7.347%   $253.9615   $253.96   $253.95   $254.00  
  Purchase #3 $11.83   13.408%   $13.4162   $13.42   $13.40   $13.40  
  Purchase #4 $36.46   7.328%   $39.1318   $39.13   $39.15   $39.10  
  Purchase #5 $166.38   5.227%   $175.0767   $175.08   $175.10   $175.10  
  Purchase #6 $9.67   6.785%   $10.3261   $10.33   $10.35   $10.30  
  Purchase #7 $84.33   13.395%   $95.626   $95.63   $95.65   $95.60  
  7 purchase totals = $714.91       $773.4483   $773.46   $773.50   $773.40