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 $224.64   7.614%   $241.7441   $241.74   $241.75   $241.70  
  Purchase #2 $236.72   13.403%   $268.4476   $268.45   $268.45   $268.40  
  Purchase #3 $177.97   13.858%   $202.6331   $202.63   $202.65   $202.60  
  Purchase #4 $85.91   12.544%   $96.6866   $96.69   $96.70   $96.70  
  Purchase #5 $30.55   9.705%   $33.5149   $33.51   $33.50   $33.50  
  Purchase #6 $231.54   12.252%   $259.9083   $259.91   $259.90   $259.90  
  Purchase #7 $140.92   11.663%   $157.3555   $157.36   $157.35   $157.40  
  7 purchase totals = $1,128.25       $1,260.2901   $1,260.29   $1,260.30   $1,260.20