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 $95.27   5.337%   $100.3546   $100.35   $100.35   $100.40  
  Purchase #2 $62.97   9.577%   $69.0006   $69.00   $69.00   $69.00  
  Purchase #3 $161.31   8.243%   $174.6068   $174.61   $174.60   $174.60  
  Purchase #4 $182.88   7.814%   $197.1702   $197.17   $197.15   $197.20  
  Purchase #5 $107.33   5.435%   $113.1634   $113.16   $113.15   $113.20  
  Purchase #6 $133.93   4.561%   $140.0385   $140.04   $140.05   $140.00  
  Purchase #7 $44.74   8.117%   $48.3715   $48.37   $48.35   $48.40  
  7 purchase totals = $788.43       $842.7056   $842.70   $842.65   $842.80