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 $89.92   13.370%   $101.9423   $101.94   $101.95   $101.90  
  Purchase #2 $38.48   7.193%   $41.2479   $41.25   $41.25   $41.20  
  Purchase #3 $233.41   9.162%   $254.795   $254.80   $254.80   $254.80  
  Purchase #4 $18.55   11.267%   $20.64   $20.64   $20.65   $20.60  
  Purchase #5 $155.33   11.467%   $173.1417   $173.14   $173.15   $173.10  
  Purchase #6 $214.64   13.446%   $243.5005   $243.50   $243.50   $243.50  
  Purchase #7 $90.97   11.741%   $101.6508   $101.65   $101.65   $101.70  
  7 purchase totals = $841.30       $936.9182   $936.92   $936.95   $936.80