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 $249.89   10.506%   $276.1434   $276.14   $276.15   $276.10  
  Purchase #2 $24.47   6.310%   $26.0141   $26.01   $26.00   $26.00  
  Purchase #3 $185.44   13.463%   $210.4058   $210.41   $210.40   $210.40  
  Purchase #4 $101.26   7.538%   $108.893   $108.89   $108.90   $108.90  
  Purchase #5 $12.86   8.719%   $13.9813   $13.98   $14.00   $14.00  
  Purchase #6 $220.61   3.560%   $228.4637   $228.46   $228.45   $228.50  
  Purchase #7 $113.27   9.352%   $123.863   $123.86   $123.85   $123.90  
  7 purchase totals = $907.80       $987.7643   $987.75   $987.75   $987.80