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 $211.66   13.629%   $240.5071   $240.51   $240.50   $240.50  
  Purchase #2 $196.57   9.350%   $214.9493   $214.95   $214.95   $214.90  
  Purchase #3 $136.59   12.273%   $153.3537   $153.35   $153.35   $153.40  
  Purchase #4 $80.38   3.105%   $82.8758   $82.88   $82.90   $82.90  
  Purchase #5 $145.48   13.661%   $165.354   $165.35   $165.35   $165.40  
  Purchase #6 $116.86   7.812%   $125.9891   $125.99   $126.00   $126.00  
  Purchase #7 $107.40   11.453%   $119.7005   $119.70   $119.70   $119.70  
  7 purchase totals = $994.94       $1,102.7295   $1,102.73   $1,102.75   $1,102.80