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 $63.85   8.128%   $69.0397   $69.04   $69.05   $69.00  
  Purchase #2 $164.31   4.320%   $171.4082   $171.41   $171.40   $171.40  
  Purchase #3 $164.90   6.351%   $175.3728   $175.37   $175.35   $175.40  
  Purchase #4 $242.56   10.309%   $267.5655   $267.57   $267.55   $267.60  
  Purchase #5 $126.75   12.190%   $142.2008   $142.20   $142.20   $142.20  
  Purchase #6 $148.66   12.556%   $167.3257   $167.33   $167.35   $167.30  
  Purchase #7 $221.80   12.620%   $249.7912   $249.79   $249.80   $249.80  
  7 purchase totals = $1,132.83       $1,242.7039   $1,242.71   $1,242.70   $1,242.70