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 $136.79   5.859%   $144.8045   $144.80   $144.80   $144.80  
  Purchase #2 $45.82   8.418%   $49.6771   $49.68   $49.70   $49.70  
  Purchase #3 $205.50   3.788%   $213.2843   $213.28   $213.30   $213.30  
  Purchase #4 $86.66   5.826%   $91.7088   $91.71   $91.70   $91.70  
  Purchase #5 $63.48   4.798%   $66.5258   $66.53   $66.55   $66.50  
  Purchase #6 $243.96   13.248%   $276.2798   $276.28   $276.30   $276.30  
  Purchase #7 $212.53   6.148%   $225.5963   $225.60   $225.60   $225.60  
  7 purchase totals = $994.74       $1,067.8766   $1,067.88   $1,067.95   $1,067.90