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 $240.35   9.278%   $262.6497   $262.65   $262.65   $262.60  
  Purchase #2 $237.39   11.490%   $264.6661   $264.67   $264.65   $264.70  
  Purchase #3 $232.92   10.723%   $257.896   $257.90   $257.90   $257.90  
  Purchase #4 $127.53   7.676%   $137.3192   $137.32   $137.30   $137.30  
  Purchase #5 $24.36   4.522%   $25.4616   $25.46   $25.45   $25.50  
  Purchase #6 $237.46   11.401%   $264.5328   $264.53   $264.55   $264.50  
  Purchase #7 $45.65   3.676%   $47.3281   $47.33   $47.35   $47.30  
  7 purchase totals = $1,145.66       $1,259.8535   $1,259.86   $1,259.85   $1,259.80