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 $168.77   13.753%   $191.9809   $191.98   $192.00   $192.00  
  Purchase #2 $76.78   10.694%   $84.9909   $84.99   $85.00   $85.00  
  Purchase #3 $215.97   10.216%   $238.0335   $238.03   $238.05   $238.00  
  Purchase #4 $49.60   6.249%   $52.6995   $52.70   $52.70   $52.70  
  Purchase #5 $104.73   7.172%   $112.2412   $112.24   $112.25   $112.20  
  Purchase #6 $164.94   13.661%   $187.4725   $187.47   $187.45   $187.50  
  Purchase #7 $110.67   8.251%   $119.8014   $119.80   $119.80   $119.80  
  7 purchase totals = $891.46       $987.2199   $987.21   $987.25   $987.20