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 $72.57   5.344%   $76.4481   $76.45   $76.45   $76.40  
  Purchase #2 $84.84   10.740%   $93.9518   $93.95   $93.95   $94.00  
  Purchase #3 $100.27   7.436%   $107.7261   $107.73   $107.75   $107.70  
  Purchase #4 $247.39   4.569%   $258.6932   $258.69   $258.70   $258.70  
  Purchase #5 $132.34   11.366%   $147.3818   $147.38   $147.40   $147.40  
  Purchase #6 $34.77   10.202%   $38.3172   $38.32   $38.30   $38.30  
  Purchase #7 $86.67   7.371%   $93.0584   $93.06   $93.05   $93.10  
  7 purchase totals = $758.85       $815.5766   $815.58   $815.60   $815.60