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 $63.49   6.535%   $67.6391   $67.64   $67.65   $67.60  
  Purchase #2 $123.42   7.705%   $132.9295   $132.93   $132.95   $132.90  
  Purchase #3 $164.47   12.259%   $184.6324   $184.63   $184.65   $184.60  
  Purchase #4 $44.55   3.556%   $46.1342   $46.13   $46.15   $46.10  
  Purchase #5 $101.65   5.416%   $107.1554   $107.16   $107.15   $107.20  
  Purchase #6 $100.49   5.115%   $105.6301   $105.63   $105.65   $105.60  
  Purchase #7 $179.77   4.625%   $188.0844   $188.08   $188.10   $188.10  
  7 purchase totals = $777.84       $832.2051   $832.20   $832.30   $832.10