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 $30.77   11.111%   $34.1889   $34.19   $34.20   $34.20  
  Purchase #2 $214.29   6.706%   $228.6603   $228.66   $228.65   $228.70  
  Purchase #3 $131.41   10.448%   $145.1397   $145.14   $145.15   $145.10  
  Purchase #4 $241.46   10.707%   $267.3131   $267.31   $267.30   $267.30  
  Purchase #5 $119.39   11.160%   $132.7139   $132.71   $132.70   $132.70  
  Purchase #6 $175.80   13.202%   $199.0091   $199.01   $199.00   $199.00  
  Purchase #7 $37.45   7.711%   $40.3378   $40.34   $40.35   $40.30  
  7 purchase totals = $950.57       $1,047.3628   $1,047.36   $1,047.35   $1,047.30