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 $95.29   6.774%   $101.7449   $101.74   $101.75   $101.70  
  Purchase #2 $190.44   4.276%   $198.5832   $198.58   $198.60   $198.60  
  Purchase #3 $98.76   6.239%   $104.9216   $104.92   $104.90   $104.90  
  Purchase #4 $114.72   10.459%   $126.7186   $126.72   $126.70   $126.70  
  Purchase #5 $168.53   9.281%   $184.1713   $184.17   $184.15   $184.20  
  Purchase #6 $193.71   12.757%   $218.4216   $218.42   $218.40   $218.40  
  Purchase #7 $66.58   3.516%   $68.921   $68.92   $68.90   $68.90  
  7 purchase totals = $928.03       $1,003.4822   $1,003.47   $1,003.40   $1,003.40