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 $240.85   13.446%   $273.2347   $273.23   $273.25   $273.20  
  Purchase #2 $174.29   3.848%   $180.9967   $181.00   $181.00   $181.00  
  Purchase #3 $56.76   8.304%   $61.4734   $61.47   $61.45   $61.50  
  Purchase #4 $76.45   13.505%   $86.7746   $86.77   $86.75   $86.80  
  Purchase #5 $25.78   6.188%   $27.3753   $27.38   $27.40   $27.40  
  Purchase #6 $107.66   3.297%   $111.2096   $111.21   $111.20   $111.20  
  Purchase #7 $21.90   13.731%   $24.9071   $24.91   $24.90   $24.90  
  7 purchase totals = $703.69       $765.9714   $765.97   $765.95   $766.00