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 $66.39   6.201%   $70.5068   $70.51   $70.50   $70.50  
  Purchase #2 $189.81   12.550%   $213.6312   $213.63   $213.65   $213.60  
  Purchase #3 $119.46   7.867%   $128.8579   $128.86   $128.85   $128.90  
  Purchase #4 $225.33   7.507%   $242.2455   $242.25   $242.25   $242.20  
  Purchase #5 $29.81   3.625%   $30.8906   $30.89   $30.90   $30.90  
  Purchase #6 $162.48   7.215%   $174.2029   $174.20   $174.20   $174.20  
  Purchase #7 $194.55   5.603%   $205.4506   $205.45   $205.45   $205.50  
  7 purchase totals = $987.83       $1,065.7855   $1,065.79   $1,065.80   $1,065.80