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 $208.55   7.825%   $224.869   $224.87   $224.85   $224.90  
  Purchase #2 $124.76   9.539%   $136.6609   $136.66   $136.65   $136.70  
  Purchase #3 $14.78   11.459%   $16.4736   $16.47   $16.45   $16.50  
  Purchase #4 $169.53   3.161%   $174.8888   $174.89   $174.90   $174.90  
  Purchase #5 $99.68   13.769%   $113.4049   $113.40   $113.40   $113.40  
  Purchase #6 $58.69   5.865%   $62.1322   $62.13   $62.15   $62.10  
  Purchase #7 $112.92   3.171%   $116.5007   $116.50   $116.50   $116.50  
  7 purchase totals = $788.91       $844.9301   $844.92   $844.90   $845.00