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 $163.47   11.728%   $182.6418   $182.64   $182.65   $182.60  
  Purchase #2 $230.34   9.494%   $252.2085   $252.21   $252.20   $252.20  
  Purchase #3 $83.62   12.547%   $94.1118   $94.11   $94.10   $94.10  
  Purchase #4 $73.30   9.690%   $80.4028   $80.40   $80.40   $80.40  
  Purchase #5 $169.71   11.318%   $188.9178   $188.92   $188.90   $188.90  
  Purchase #6 $192.54   3.725%   $199.7121   $199.71   $199.70   $199.70  
  Purchase #7 $50.46   9.733%   $55.3713   $55.37   $55.35   $55.40  
  7 purchase totals = $963.44       $1,053.3661   $1,053.36   $1,053.30   $1,053.30