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 $101.89   10.235%   $112.3184   $112.32   $112.30   $112.30  
  Purchase #2 $245.33   12.362%   $275.6577   $275.66   $275.65   $275.70  
  Purchase #3 $62.43   10.812%   $69.1799   $69.18   $69.20   $69.20  
  Purchase #4 $242.32   10.582%   $267.9623   $267.96   $267.95   $268.00  
  Purchase #5 $26.85   11.867%   $30.0363   $30.04   $30.05   $30.00  
  Purchase #6 $181.96   7.583%   $195.758   $195.76   $195.75   $195.80  
  Purchase #7 $206.41   5.366%   $217.486   $217.49   $217.50   $217.50  
  7 purchase totals = $1,067.19       $1,168.3986   $1,168.41   $1,168.40   $1,168.50