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 $66.39   10.791%   $73.5541   $73.55   $73.55   $73.60  
  Purchase #2 $182.76   4.113%   $190.2769   $190.28   $190.30   $190.30  
  Purchase #3 $184.68   5.240%   $194.3572   $194.36   $194.35   $194.40  
  Purchase #4 $159.58   5.841%   $168.9011   $168.90   $168.90   $168.90  
  Purchase #5 $93.57   8.204%   $101.2465   $101.25   $101.25   $101.20  
  Purchase #6 $170.76   13.531%   $193.8655   $193.87   $193.85   $193.90  
  Purchase #7 $177.29   6.612%   $189.0124   $189.01   $189.00   $189.00  
  7 purchase totals = $1,035.03       $1,111.2137   $1,111.22   $1,111.20   $1,111.30