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 $88.37   6.106%   $93.7659   $93.77   $93.75   $93.80  
  Purchase #2 $231.62   6.489%   $246.6498   $246.65   $246.65   $246.60  
  Purchase #3 $111.87   5.614%   $118.1504   $118.15   $118.15   $118.20  
  Purchase #4 $189.25   5.407%   $199.4827   $199.48   $199.50   $199.50  
  Purchase #5 $132.81   10.456%   $146.6966   $146.70   $146.70   $146.70  
  Purchase #6 $64.37   12.726%   $72.5617   $72.56   $72.55   $72.60  
  Purchase #7 $236.69   7.145%   $253.6015   $253.60   $253.60   $253.60  
  7 purchase totals = $1,054.98       $1,130.9086   $1,130.91   $1,130.90   $1,131.00