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 $154.48   5.723%   $163.3209   $163.32   $163.30   $163.30  
  Purchase #2 $244.74   9.433%   $267.8263   $267.83   $267.85   $267.80  
  Purchase #3 $51.57   9.631%   $56.5367   $56.54   $56.55   $56.50  
  Purchase #4 $94.90   6.837%   $101.3883   $101.39   $101.40   $101.40  
  Purchase #5 $125.35   4.631%   $131.155   $131.16   $131.15   $131.20  
  Purchase #6 $218.28   12.283%   $245.0913   $245.09   $245.10   $245.10  
  Purchase #7 $104.80   9.268%   $114.5129   $114.51   $114.50   $114.50  
  7 purchase totals = $994.12       $1,079.8314   $1,079.84   $1,079.85   $1,079.80