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 $248.59   10.433%   $274.5254   $274.53   $274.55   $274.50  
  Purchase #2 $205.27   6.591%   $218.7993   $218.80   $218.80   $218.80  
  Purchase #3 $212.32   4.811%   $222.5347   $222.53   $222.55   $222.50  
  Purchase #4 $53.36   5.841%   $56.4768   $56.48   $56.50   $56.50  
  Purchase #5 $118.63   11.525%   $132.3021   $132.30   $132.30   $132.30  
  Purchase #6 $97.60   3.686%   $101.1975   $101.20   $101.20   $101.20  
  Purchase #7 $29.43   8.202%   $31.8438   $31.84   $31.85   $31.80  
  7 purchase totals = $965.20       $1,037.6796   $1,037.68   $1,037.75   $1,037.60