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 $184.44   6.170%   $195.8199   $195.82   $195.80   $195.80  
  Purchase #2 $149.87   3.229%   $154.7093   $154.71   $154.70   $154.70  
  Purchase #3 $129.98   5.207%   $136.7481   $136.75   $136.75   $136.70  
  Purchase #4 $141.46   6.709%   $150.9506   $150.95   $150.95   $151.00  
  Purchase #5 $217.79   7.551%   $234.2353   $234.24   $234.25   $234.20  
  Purchase #6 $229.58   5.367%   $241.9016   $241.90   $241.90   $241.90  
  Purchase #7 $189.83   5.455%   $200.1852   $200.19   $200.20   $200.20  
  7 purchase totals = $1,242.95       $1,314.5500   $1,314.56   $1,314.55   $1,314.50