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 $208.59   11.556%   $232.6947   $232.69   $232.70   $232.70  
  Purchase #2 $235.64   4.372%   $245.9422   $245.94   $245.95   $245.90  
  Purchase #3 $141.63   7.170%   $151.7849   $151.78   $151.80   $151.80  
  Purchase #4 $241.82   4.274%   $252.1554   $252.16   $252.15   $252.20  
  Purchase #5 $193.26   6.279%   $205.3948   $205.39   $205.40   $205.40  
  Purchase #6 $206.64   5.487%   $217.9783   $217.98   $218.00   $218.00  
  Purchase #7 $133.83   7.778%   $144.2393   $144.24   $144.25   $144.20  
  7 purchase totals = $1,361.41       $1,450.1896   $1,450.18   $1,450.25   $1,450.20