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 $218.34   7.751%   $235.2635   $235.26   $235.25   $235.30  
  Purchase #2 $117.90   4.848%   $123.6158   $123.62   $123.60   $123.60  
  Purchase #3 $161.87   5.409%   $170.6255   $170.63   $170.65   $170.60  
  Purchase #4 $102.25   4.778%   $107.1355   $107.14   $107.15   $107.10  
  Purchase #5 $98.69   9.272%   $107.8405   $107.84   $107.85   $107.80  
  Purchase #6 $157.71   5.242%   $165.9772   $165.98   $166.00   $166.00  
  Purchase #7 $28.58   7.258%   $30.6543   $30.65   $30.65   $30.70  
  7 purchase totals = $885.34       $941.1123   $941.12   $941.15   $941.10