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 $93.25   3.372%   $96.3944   $96.39   $96.40   $96.40  
  Purchase #2 $161.64   11.566%   $180.3353   $180.34   $180.35   $180.30  
  Purchase #3 $152.87   7.554%   $164.4178   $164.42   $164.40   $164.40  
  Purchase #4 $203.75   4.319%   $212.55   $212.55   $212.55   $212.60  
  Purchase #5 $55.61   5.582%   $58.7142   $58.71   $58.70   $58.70  
  Purchase #6 $99.48   6.396%   $105.8427   $105.84   $105.85   $105.80  
  Purchase #7 $119.70   12.185%   $134.2854   $134.29   $134.30   $134.30  
  7 purchase totals = $886.30       $952.5398   $952.54   $952.55   $952.50