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 $76.50   13.230%   $86.621   $86.62   $86.60   $86.60  
  Purchase #2 $187.55   3.496%   $194.1067   $194.11   $194.10   $194.10  
  Purchase #3 $215.38   5.844%   $227.9668   $227.97   $227.95   $228.00  
  Purchase #4 $187.70   9.783%   $206.0627   $206.06   $206.05   $206.10  
  Purchase #5 $78.57   11.447%   $87.5639   $87.56   $87.55   $87.60  
  Purchase #6 $155.76   6.734%   $166.2489   $166.25   $166.25   $166.20  
  Purchase #7 $96.61   9.325%   $105.6189   $105.62   $105.60   $105.60  
  7 purchase totals = $998.07       $1,074.1889   $1,074.19   $1,074.10   $1,074.20