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 $49.44   13.423%   $56.0763   $56.08   $56.10   $56.10  
  Purchase #2 $191.42   8.242%   $207.1968   $207.20   $207.20   $207.20  
  Purchase #3 $115.38   9.511%   $126.3538   $126.35   $126.35   $126.40  
  Purchase #4 $212.59   8.707%   $231.1002   $231.10   $231.10   $231.10  
  Purchase #5 $109.59   5.506%   $115.624   $115.62   $115.60   $115.60  
  Purchase #6 $152.92   8.788%   $166.3586   $166.36   $166.35   $166.40  
  Purchase #7 $197.41   11.214%   $219.5476   $219.55   $219.55   $219.50  
  7 purchase totals = $1,028.75       $1,122.2573   $1,122.26   $1,122.25   $1,122.30