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 $227.27   11.726%   $253.9197   $253.92   $253.90   $253.90  
  Purchase #2 $155.90   11.252%   $173.4419   $173.44   $173.45   $173.40  
  Purchase #3 $168.53   4.790%   $176.6026   $176.60   $176.60   $176.60  
  Purchase #4 $103.98   10.732%   $115.1391   $115.14   $115.15   $115.10  
  Purchase #5 $101.50   6.638%   $108.2376   $108.24   $108.25   $108.20  
  Purchase #6 $191.53   11.572%   $213.6939   $213.69   $213.70   $213.70  
  Purchase #7 $8.38   9.259%   $9.1559   $9.16   $9.15   $9.20  
  7 purchase totals = $957.09       $1,050.1907   $1,050.19   $1,050.20   $1,050.10