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 $84.55   12.507%   $95.1247   $95.12   $95.10   $95.10  
  Purchase #2 $183.44   11.559%   $204.6438   $204.64   $204.65   $204.60  
  Purchase #3 $183.97   9.784%   $201.9696   $201.97   $201.95   $202.00  
  Purchase #4 $86.71   8.674%   $94.2312   $94.23   $94.25   $94.20  
  Purchase #5 $98.74   10.407%   $109.0159   $109.02   $109.00   $109.00  
  Purchase #6 $168.94   5.510%   $178.2486   $178.25   $178.25   $178.20  
  Purchase #7 $96.81   5.235%   $101.878   $101.88   $101.90   $101.90  
  7 purchase totals = $903.16       $985.1118   $985.11   $985.10   $985.00