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 $64.46   6.241%   $68.4829   $68.48   $68.50   $68.50  
  Purchase #2 $105.26   11.586%   $117.4554   $117.46   $117.45   $117.50  
  Purchase #3 $102.42   4.443%   $106.9705   $106.97   $106.95   $107.00  
  Purchase #4 $164.99   6.361%   $175.485   $175.49   $175.50   $175.50  
  Purchase #5 $174.59   7.832%   $188.2639   $188.26   $188.25   $188.30  
  Purchase #6 $144.84   6.834%   $154.7384   $154.74   $154.75   $154.70  
  Purchase #7 $57.91   13.849%   $65.93   $65.93   $65.95   $65.90  
  7 purchase totals = $814.47       $877.3261   $877.33   $877.35   $877.40