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 $32.29   4.252%   $33.663   $33.66   $33.65   $33.70  
  Purchase #2 $85.33   9.342%   $93.3015   $93.30   $93.30   $93.30  
  Purchase #3 $31.80   8.744%   $34.5806   $34.58   $34.60   $34.60  
  Purchase #4 $120.62   7.705%   $129.9138   $129.91   $129.90   $129.90  
  Purchase #5 $249.73   6.772%   $266.6417   $266.64   $266.65   $266.60  
  Purchase #6 $197.78   4.105%   $205.8989   $205.90   $205.90   $205.90  
  Purchase #7 $113.46   13.577%   $128.8645   $128.86   $128.85   $128.90  
  7 purchase totals = $831.01       $892.8640   $892.85   $892.85   $892.90