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 $60.79   12.459%   $68.3638   $68.36   $68.35   $68.40  
  Purchase #2 $34.44   6.712%   $36.7516   $36.75   $36.75   $36.80  
  Purchase #3 $14.70   8.409%   $15.9361   $15.94   $15.95   $15.90  
  Purchase #4 $127.60   5.592%   $134.7354   $134.74   $134.75   $134.70  
  Purchase #5 $148.25   11.258%   $164.94   $164.94   $164.95   $164.90  
  Purchase #6 $160.88   7.734%   $173.3225   $173.32   $173.30   $173.30  
  Purchase #7 $168.25   13.231%   $190.5112   $190.51   $190.50   $190.50  
  7 purchase totals = $714.91       $784.5606   $784.56   $784.55   $784.50