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 $66.61   4.721%   $69.7547   $69.75   $69.75   $69.80  
  Purchase #2 $80.64   6.586%   $85.951   $85.95   $85.95   $86.00  
  Purchase #3 $20.43   4.658%   $21.3816   $21.38   $21.40   $21.40  
  Purchase #4 $211.53   3.149%   $218.1911   $218.19   $218.20   $218.20  
  Purchase #5 $24.32   12.754%   $27.4218   $27.42   $27.40   $27.40  
  Purchase #6 $231.69   10.776%   $256.6569   $256.66   $256.65   $256.70  
  Purchase #7 $244.78   3.311%   $252.8847   $252.88   $252.90   $252.90  
  7 purchase totals = $880.00       $932.2418   $932.23   $932.25   $932.40