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 $173.42   3.313%   $179.1654   $179.17   $179.15   $179.20  
  Purchase #2 $159.64   3.127%   $164.6319   $164.63   $164.65   $164.60  
  Purchase #3 $177.88   9.196%   $194.2378   $194.24   $194.25   $194.20  
  Purchase #4 $130.65   3.503%   $135.2267   $135.23   $135.25   $135.20  
  Purchase #5 $168.48   5.235%   $177.2999   $177.30   $177.30   $177.30  
  Purchase #6 $44.37   10.791%   $49.158   $49.16   $49.15   $49.20  
  Purchase #7 $212.93   13.612%   $241.914   $241.91   $241.90   $241.90  
  7 purchase totals = $1,067.37       $1,141.6337   $1,141.64   $1,141.65   $1,141.60