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 $67.69   8.234%   $73.2636   $73.26   $73.25   $73.30  
  Purchase #2 $27.76   7.432%   $29.8231   $29.82   $29.80   $29.80  
  Purchase #3 $152.79   8.770%   $166.1897   $166.19   $166.20   $166.20  
  Purchase #4 $162.98   6.170%   $173.0359   $173.04   $173.05   $173.00  
  Purchase #5 $116.76   9.547%   $127.9071   $127.91   $127.90   $127.90  
  Purchase #6 $240.89   3.410%   $249.1043   $249.10   $249.10   $249.10  
  Purchase #7 $193.25   3.576%   $200.1606   $200.16   $200.15   $200.20  
  7 purchase totals = $962.12       $1,019.4843   $1,019.48   $1,019.45   $1,019.50