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 $131.87   10.719%   $146.0051   $146.01   $146.00   $146.00  
  Purchase #2 $24.87   12.160%   $27.8942   $27.89   $27.90   $27.90  
  Purchase #3 $183.59   12.599%   $206.7205   $206.72   $206.70   $206.70  
  Purchase #4 $233.27   13.240%   $264.1549   $264.15   $264.15   $264.20  
  Purchase #5 $99.75   13.206%   $112.923   $112.92   $112.90   $112.90  
  Purchase #6 $180.71   9.479%   $197.8395   $197.84   $197.85   $197.80  
  Purchase #7 $233.25   6.810%   $249.1343   $249.13   $249.15   $249.10  
  7 purchase totals = $1,087.31       $1,204.6715   $1,204.66   $1,204.65   $1,204.60