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 $78.58   11.867%   $87.9051   $87.91   $87.90   $87.90  
  Purchase #2 $129.55   6.558%   $138.0459   $138.05   $138.05   $138.00  
  Purchase #3 $20.82   12.494%   $23.4213   $23.42   $23.40   $23.40  
  Purchase #4 $232.97   6.509%   $248.134   $248.13   $248.15   $248.10  
  Purchase #5 $91.32   11.268%   $101.6099   $101.61   $101.60   $101.60  
  Purchase #6 $112.32   7.137%   $120.3363   $120.34   $120.35   $120.30  
  Purchase #7 $43.32   8.853%   $47.1551   $47.16   $47.15   $47.20  
  7 purchase totals = $708.88       $766.6076   $766.62   $766.60   $766.50