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 $47.81   11.738%   $53.4219   $53.42   $53.40   $53.40  
  Purchase #2 $164.94   4.339%   $172.0967   $172.10   $172.10   $172.10  
  Purchase #3 $214.29   13.376%   $242.9534   $242.95   $242.95   $243.00  
  Purchase #4 $182.46   13.464%   $207.0264   $207.03   $207.05   $207.00  
  Purchase #5 $235.81   12.515%   $265.3216   $265.32   $265.30   $265.30  
  Purchase #6 $182.44   10.667%   $201.9009   $201.90   $201.90   $201.90  
  Purchase #7 $115.92   12.822%   $130.7833   $130.78   $130.80   $130.80  
  7 purchase totals = $1,143.67       $1,273.5042   $1,273.50   $1,273.50   $1,273.50