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 $174.73   12.299%   $196.22   $196.22   $196.20   $196.20  
  Purchase #2 $179.55   5.682%   $189.752   $189.75   $189.75   $189.80  
  Purchase #3 $159.72   6.233%   $169.6753   $169.68   $169.70   $169.70  
  Purchase #4 $213.72   9.506%   $234.0362   $234.04   $234.05   $234.00  
  Purchase #5 $13.68   10.255%   $15.0829   $15.08   $15.10   $15.10  
  Purchase #6 $207.64   11.793%   $232.127   $232.13   $232.15   $232.10  
  Purchase #7 $222.33   9.189%   $242.7599   $242.76   $242.75   $242.80  
  7 purchase totals = $1,171.37       $1,279.6533   $1,279.66   $1,279.70   $1,279.70