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 $72.71   13.314%   $82.3906   $82.39   $82.40   $82.40  
  Purchase #2 $183.37   13.412%   $207.9636   $207.96   $207.95   $208.00  
  Purchase #3 $98.55   11.442%   $109.8261   $109.83   $109.85   $109.80  
  Purchase #4 $113.80   6.752%   $121.4838   $121.48   $121.50   $121.50  
  Purchase #5 $208.92   8.356%   $226.3774   $226.38   $226.40   $226.40  
  Purchase #6 $28.63   8.209%   $30.9802   $30.98   $31.00   $31.00  
  Purchase #7 $244.58   12.309%   $274.6854   $274.69   $274.70   $274.70  
  7 purchase totals = $950.56       $1,053.7071   $1,053.71   $1,053.80   $1,053.80