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 $105.33   8.791%   $114.5896   $114.59   $114.60   $114.60  
  Purchase #2 $218.86   8.414%   $237.2749   $237.27   $237.25   $237.30  
  Purchase #3 $236.45   13.254%   $267.7891   $267.79   $267.80   $267.80  
  Purchase #4 $56.73   8.655%   $61.64   $61.64   $61.65   $61.60  
  Purchase #5 $124.65   11.643%   $139.163   $139.16   $139.15   $139.20  
  Purchase #6 $141.40   11.338%   $157.4319   $157.43   $157.45   $157.40  
  Purchase #7 $90.53   12.560%   $101.9006   $101.90   $101.90   $101.90  
  7 purchase totals = $973.95       $1,079.7891   $1,079.78   $1,079.80   $1,079.80