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 $24.89   4.226%   $25.9419   $25.94   $25.95   $25.90  
  Purchase #2 $202.37   12.605%   $227.8787   $227.88   $227.90   $227.90  
  Purchase #3 $129.78   4.852%   $136.0769   $136.08   $136.10   $136.10  
  Purchase #4 $30.67   12.150%   $34.3964   $34.40   $34.40   $34.40  
  Purchase #5 $242.76   6.773%   $259.2021   $259.20   $259.20   $259.20  
  Purchase #6 $146.58   5.571%   $154.746   $154.75   $154.75   $154.70  
  Purchase #7 $248.97   11.469%   $277.5244   $277.52   $277.50   $277.50  
  7 purchase totals = $1,026.02       $1,115.7664   $1,115.77   $1,115.80   $1,115.70