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 $92.87   5.448%   $97.9296   $97.93   $97.95   $97.90  
  Purchase #2 $72.70   13.161%   $82.268   $82.27   $82.25   $82.30  
  Purchase #3 $33.95   13.737%   $38.6137   $38.61   $38.60   $38.60  
  Purchase #4 $110.77   12.259%   $124.3493   $124.35   $124.35   $124.30  
  Purchase #5 $246.76   12.369%   $277.2817   $277.28   $277.30   $277.30  
  Purchase #6 $144.60   6.607%   $154.1537   $154.15   $154.15   $154.20  
  Purchase #7 $84.36   4.741%   $88.3595   $88.36   $88.35   $88.40  
  7 purchase totals = $786.01       $862.9555   $862.95   $862.95   $863.00