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 $126.81   11.195%   $141.0064   $141.01   $141.00   $141.00  
  Purchase #2 $191.91   4.816%   $201.1524   $201.15   $201.15   $201.20  
  Purchase #3 $82.67   7.536%   $88.9   $88.90   $88.90   $88.90  
  Purchase #4 $70.26   4.681%   $73.5489   $73.55   $73.55   $73.50  
  Purchase #5 $44.42   7.547%   $47.7724   $47.77   $47.75   $47.80  
  Purchase #6 $171.84   13.306%   $194.705   $194.71   $194.70   $194.70  
  Purchase #7 $248.67   9.626%   $272.607   $272.61   $272.60   $272.60  
  7 purchase totals = $936.58       $1,019.6921   $1,019.70   $1,019.65   $1,019.70