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 $76.93   9.331%   $84.1083   $84.11   $84.10   $84.10  
  Purchase #2 $92.88   4.862%   $97.3958   $97.40   $97.40   $97.40  
  Purchase #3 $115.69   10.378%   $127.6963   $127.70   $127.70   $127.70  
  Purchase #4 $246.28   8.516%   $267.2532   $267.25   $267.25   $267.30  
  Purchase #5 $33.62   4.441%   $35.1131   $35.11   $35.10   $35.10  
  Purchase #6 $209.97   6.693%   $224.0233   $224.02   $224.00   $224.00  
  Purchase #7 $51.84   9.589%   $56.8109   $56.81   $56.80   $56.80  
  7 purchase totals = $827.21       $892.4009   $892.40   $892.35   $892.40