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 $239.73   11.317%   $266.8602   $266.86   $266.85   $266.90  
  Purchase #2 $226.41   10.125%   $249.334   $249.33   $249.35   $249.30  
  Purchase #3 $246.63   4.140%   $256.8405   $256.84   $256.85   $256.80  
  Purchase #4 $136.70   7.279%   $146.6504   $146.65   $146.65   $146.70  
  Purchase #5 $54.77   12.337%   $61.527   $61.53   $61.55   $61.50  
  Purchase #6 $80.90   3.133%   $83.4346   $83.43   $83.45   $83.40  
  Purchase #7 $107.41   9.811%   $117.948   $117.95   $117.95   $117.90  
  7 purchase totals = $1,092.55       $1,182.5947   $1,182.59   $1,182.65   $1,182.50