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 $88.28   4.736%   $92.4609   $92.46   $92.45   $92.50  
  Purchase #2 $22.87   3.445%   $23.6579   $23.66   $23.65   $23.70  
  Purchase #3 $95.90   4.535%   $100.2491   $100.25   $100.25   $100.20  
  Purchase #4 $199.31   6.249%   $211.7649   $211.76   $211.75   $211.80  
  Purchase #5 $154.81   3.823%   $160.7284   $160.73   $160.75   $160.70  
  Purchase #6 $46.39   5.376%   $48.8839   $48.88   $48.90   $48.90  
  Purchase #7 $184.88   3.442%   $191.2436   $191.24   $191.25   $191.20  
  7 purchase totals = $792.44       $828.9887   $828.98   $829.00   $829.00