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 $124.79   6.579%   $132.9999   $133.00   $133.00   $133.00  
  Purchase #2 $43.83   6.589%   $46.718   $46.72   $46.70   $46.70  
  Purchase #3 $205.84   6.244%   $218.6926   $218.69   $218.70   $218.70  
  Purchase #4 $140.42   12.508%   $157.9837   $157.98   $158.00   $158.00  
  Purchase #5 $88.36   9.596%   $96.839   $96.84   $96.85   $96.80  
  Purchase #6 $249.65   3.154%   $257.524   $257.52   $257.50   $257.50  
  Purchase #7 $94.33   12.248%   $105.8835   $105.88   $105.90   $105.90  
  7 purchase totals = $947.22       $1,016.6407   $1,016.63   $1,016.65   $1,016.60