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 $58.27   10.162%   $64.1914   $64.19   $64.20   $64.20  
  Purchase #2 $194.57   5.178%   $204.6448   $204.64   $204.65   $204.60  
  Purchase #3 $29.65   8.531%   $32.1794   $32.18   $32.20   $32.20  
  Purchase #4 $164.65   12.703%   $185.5655   $185.57   $185.55   $185.60  
  Purchase #5 $142.25   8.543%   $154.4024   $154.40   $154.40   $154.40  
  Purchase #6 $249.28   3.135%   $257.0949   $257.09   $257.10   $257.10  
  Purchase #7 $146.46   3.144%   $151.0647   $151.06   $151.05   $151.10  
  7 purchase totals = $985.13       $1,049.1431   $1,049.13   $1,049.15   $1,049.20