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 $215.43   13.272%   $244.0219   $244.02   $244.00   $244.00  
  Purchase #2 $73.43   3.756%   $76.188   $76.19   $76.20   $76.20  
  Purchase #3 $79.89   7.382%   $85.7875   $85.79   $85.80   $85.80  
  Purchase #4 $238.83   10.814%   $264.6571   $264.66   $264.65   $264.70  
  Purchase #5 $162.58   9.154%   $177.4626   $177.46   $177.45   $177.50  
  Purchase #6 $10.37   13.781%   $11.7991   $11.80   $11.80   $11.80  
  Purchase #7 $142.48   6.477%   $151.7084   $151.71   $151.70   $151.70  
  7 purchase totals = $923.01       $1,011.6246   $1,011.63   $1,011.60   $1,011.70