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 $212.52   6.605%   $226.5569   $226.56   $226.55   $226.60  
  Purchase #2 $101.55   11.455%   $113.1826   $113.18   $113.20   $113.20  
  Purchase #3 $113.91   3.511%   $117.9094   $117.91   $117.90   $117.90  
  Purchase #4 $188.62   13.180%   $213.4801   $213.48   $213.50   $213.50  
  Purchase #5 $134.66   10.143%   $148.3186   $148.32   $148.30   $148.30  
  Purchase #6 $167.50   9.443%   $183.317   $183.32   $183.30   $183.30  
  Purchase #7 $221.93   11.106%   $246.5775   $246.58   $246.60   $246.60  
  7 purchase totals = $1,140.69       $1,249.3421   $1,249.35   $1,249.35   $1,249.40