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 $234.87   4.583%   $245.6341   $245.63   $245.65   $245.60  
  Purchase #2 $102.87   6.499%   $109.5555   $109.56   $109.55   $109.60  
  Purchase #3 $8.80   4.604%   $9.2052   $9.21   $9.20   $9.20  
  Purchase #4 $33.84   6.620%   $36.0802   $36.08   $36.10   $36.10  
  Purchase #5 $196.73   8.503%   $213.458   $213.46   $213.45   $213.50  
  Purchase #6 $176.81   6.541%   $188.3751   $188.38   $188.40   $188.40  
  Purchase #7 $113.37   11.616%   $126.5391   $126.54   $126.55   $126.50  
  7 purchase totals = $867.29       $928.8472   $928.86   $928.90   $928.90