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 $249.53   5.343%   $262.8624   $262.86   $262.85   $262.90  
  Purchase #2 $244.43   3.774%   $253.6548   $253.65   $253.65   $253.70  
  Purchase #3 $209.89   5.675%   $221.8013   $221.80   $221.80   $221.80  
  Purchase #4 $105.32   11.140%   $117.0526   $117.05   $117.05   $117.10  
  Purchase #5 $66.90   7.635%   $72.0078   $72.01   $72.00   $72.00  
  Purchase #6 $197.53   7.227%   $211.8055   $211.81   $211.80   $211.80  
  Purchase #7 $140.42   11.102%   $156.0094   $156.01   $156.00   $156.00  
  7 purchase totals = $1,214.02       $1,295.1938   $1,295.19   $1,295.15   $1,295.30