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 $60.81   9.140%   $66.368   $66.37   $66.35   $66.40  
  Purchase #2 $92.87   8.691%   $100.9413   $100.94   $100.95   $100.90  
  Purchase #3 $15.62   11.181%   $17.3665   $17.37   $17.35   $17.40  
  Purchase #4 $96.38   9.634%   $105.6652   $105.67   $105.65   $105.70  
  Purchase #5 $43.65   13.458%   $49.5244   $49.52   $49.50   $49.50  
  Purchase #6 $166.43   9.349%   $181.9895   $181.99   $182.00   $182.00  
  Purchase #7 $178.66   7.605%   $192.2471   $192.25   $192.25   $192.20  
  7 purchase totals = $654.42       $714.1020   $714.11   $714.05   $714.10