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 $201.42   6.127%   $213.761   $213.76   $213.75   $213.80  
  Purchase #2 $240.37   3.131%   $247.896   $247.90   $247.90   $247.90  
  Purchase #3 $173.32   8.395%   $187.8702   $187.87   $187.85   $187.90  
  Purchase #4 $111.30   4.435%   $116.2362   $116.24   $116.25   $116.20  
  Purchase #5 $200.47   9.705%   $219.9256   $219.93   $219.95   $219.90  
  Purchase #6 $231.82   5.834%   $245.3444   $245.34   $245.35   $245.30  
  Purchase #7 $62.50   6.308%   $66.4425   $66.44   $66.45   $66.40  
  7 purchase totals = $1,221.20       $1,297.4759   $1,297.48   $1,297.50   $1,297.40