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 $229.47   7.241%   $246.0859   $246.09   $246.10   $246.10  
  Purchase #2 $118.56   5.663%   $125.2741   $125.27   $125.25   $125.30  
  Purchase #3 $212.70   9.485%   $232.8746   $232.87   $232.85   $232.90  
  Purchase #4 $165.47   10.826%   $183.3838   $183.38   $183.40   $183.40  
  Purchase #5 $211.63   7.277%   $227.0303   $227.03   $227.05   $227.00  
  Purchase #6 $214.99   12.438%   $241.7305   $241.73   $241.75   $241.70  
  Purchase #7 $59.89   6.535%   $63.8038   $63.80   $63.80   $63.80  
  7 purchase totals = $1,212.71       $1,320.1830   $1,320.17   $1,320.20   $1,320.20