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 $181.39   13.751%   $206.3329   $206.33   $206.35   $206.30  
  Purchase #2 $240.54   10.661%   $266.184   $266.18   $266.20   $266.20  
  Purchase #3 $122.34   7.497%   $131.5118   $131.51   $131.50   $131.50  
  Purchase #4 $195.33   7.561%   $210.0989   $210.10   $210.10   $210.10  
  Purchase #5 $153.99   5.125%   $161.882   $161.88   $161.90   $161.90  
  Purchase #6 $188.63   7.145%   $202.1076   $202.11   $202.10   $202.10  
  Purchase #7 $62.31   3.754%   $64.6491   $64.65   $64.65   $64.60  
  7 purchase totals = $1,144.53       $1,242.7663   $1,242.76   $1,242.80   $1,242.70