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 $32.49   13.665%   $36.9298   $36.93   $36.95   $36.90  
  Purchase #2 $250.44   10.204%   $275.9949   $275.99   $276.00   $276.00  
  Purchase #3 $174.25   11.328%   $193.989   $193.99   $194.00   $194.00  
  Purchase #4 $98.71   8.105%   $106.7104   $106.71   $106.70   $106.70  
  Purchase #5 $175.57   13.122%   $198.6083   $198.61   $198.60   $198.60  
  Purchase #6 $226.64   5.411%   $238.9035   $238.90   $238.90   $238.90  
  Purchase #7 $221.52   5.620%   $233.9694   $233.97   $233.95   $234.00  
  7 purchase totals = $1,179.62       $1,285.1053   $1,285.10   $1,285.10   $1,285.10