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 $67.47   9.427%   $73.8304   $73.83   $73.85   $73.80  
  Purchase #2 $75.47   13.120%   $85.3717   $85.37   $85.35   $85.40  
  Purchase #3 $222.31   8.427%   $241.0441   $241.04   $241.05   $241.00  
  Purchase #4 $205.78   8.178%   $222.6087   $222.61   $222.60   $222.60  
  Purchase #5 $58.31   8.726%   $63.3981   $63.40   $63.40   $63.40  
  Purchase #6 $231.42   5.851%   $244.9604   $244.96   $244.95   $245.00  
  Purchase #7 $229.87   8.612%   $249.6664   $249.67   $249.65   $249.70  
  7 purchase totals = $1,090.63       $1,180.8798   $1,180.88   $1,180.85   $1,180.90