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 $246.86   9.337%   $269.9093   $269.91   $269.90   $269.90  
  Purchase #2 $44.92   7.623%   $48.3443   $48.34   $48.35   $48.30  
  Purchase #3 $117.54   13.231%   $133.0917   $133.09   $133.10   $133.10  
  Purchase #4 $175.71   12.603%   $197.8547   $197.85   $197.85   $197.90  
  Purchase #5 $85.31   7.753%   $91.9241   $91.92   $91.90   $91.90  
  Purchase #6 $141.77   8.755%   $154.182   $154.18   $154.20   $154.20  
  Purchase #7 $44.73   6.670%   $47.7135   $47.71   $47.70   $47.70  
  7 purchase totals = $856.84       $943.0196   $943.00   $943.00   $943.00