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 $119.83   9.343%   $131.0257   $131.03   $131.05   $131.00  
  Purchase #2 $180.56   8.304%   $195.5537   $195.55   $195.55   $195.60  
  Purchase #3 $128.76   13.874%   $146.6242   $146.62   $146.60   $146.60  
  Purchase #4 $182.97   9.265%   $199.9222   $199.92   $199.90   $199.90  
  Purchase #5 $210.58   5.736%   $222.6589   $222.66   $222.65   $222.70  
  Purchase #6 $242.87   13.145%   $274.7953   $274.80   $274.80   $274.80  
  Purchase #7 $110.89   12.146%   $124.3587   $124.36   $124.35   $124.40  
  7 purchase totals = $1,176.46       $1,294.9387   $1,294.94   $1,294.90   $1,295.00