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 $167.69   7.165%   $179.705   $179.71   $179.70   $179.70  
  Purchase #2 $210.30   3.592%   $217.854   $217.85   $217.85   $217.90  
  Purchase #3 $233.90   10.157%   $257.6572   $257.66   $257.65   $257.70  
  Purchase #4 $13.26   4.464%   $13.8519   $13.85   $13.85   $13.90  
  Purchase #5 $109.81   6.599%   $117.0564   $117.06   $117.05   $117.10  
  Purchase #6 $24.76   8.561%   $26.8797   $26.88   $26.90   $26.90  
  Purchase #7 $241.81   6.204%   $256.8119   $256.81   $256.80   $256.80  
  7 purchase totals = $1,001.53       $1,069.8161   $1,069.82   $1,069.80   $1,070.00