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 $40.63   13.184%   $45.9867   $45.99   $46.00   $46.00  
  Purchase #2 $124.68   10.176%   $137.3674   $137.37   $137.35   $137.40  
  Purchase #3 $112.82   8.137%   $122.0002   $122.00   $122.00   $122.00  
  Purchase #4 $98.41   3.563%   $101.9163   $101.92   $101.90   $101.90  
  Purchase #5 $220.33   10.690%   $243.8833   $243.88   $243.90   $243.90  
  Purchase #6 $230.41   9.817%   $253.0293   $253.03   $253.05   $253.00  
  Purchase #7 $118.76   8.630%   $129.009   $129.01   $129.00   $129.00  
  7 purchase totals = $946.04       $1,033.1922   $1,033.20   $1,033.20   $1,033.20