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 $167.90   6.266%   $178.4206   $178.42   $178.40   $178.40  
  Purchase #2 $249.44   11.314%   $277.6616   $277.66   $277.65   $277.70  
  Purchase #3 $88.68   5.552%   $93.6035   $93.60   $93.60   $93.60  
  Purchase #4 $170.64   13.460%   $193.6081   $193.61   $193.60   $193.60  
  Purchase #5 $70.39   7.109%   $75.394   $75.39   $75.40   $75.40  
  Purchase #6 $185.62   11.427%   $206.8308   $206.83   $206.85   $206.80  
  Purchase #7 $155.25   10.622%   $171.7407   $171.74   $171.75   $171.70  
  7 purchase totals = $1,087.92       $1,197.2593   $1,197.25   $1,197.25   $1,197.20