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 $186.63   10.721%   $206.6386   $206.64   $206.65   $206.60  
  Purchase #2 $249.29   10.519%   $275.5128   $275.51   $275.50   $275.50  
  Purchase #3 $33.43   9.536%   $36.6179   $36.62   $36.60   $36.60  
  Purchase #4 $61.62   8.517%   $66.8682   $66.87   $66.85   $66.90  
  Purchase #5 $249.81   4.526%   $261.1164   $261.12   $261.10   $261.10  
  Purchase #6 $204.37   11.788%   $228.4611   $228.46   $228.45   $228.50  
  Purchase #7 $24.33   11.440%   $27.1134   $27.11   $27.10   $27.10  
  7 purchase totals = $1,009.48       $1,102.3284   $1,102.33   $1,102.25   $1,102.30