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 $126.69   12.342%   $142.3261   $142.33   $142.35   $142.30  
  Purchase #2 $193.63   4.262%   $201.8825   $201.88   $201.90   $201.90  
  Purchase #3 $127.67   5.787%   $135.0583   $135.06   $135.05   $135.10  
  Purchase #4 $26.69   12.253%   $29.9603   $29.96   $29.95   $30.00  
  Purchase #5 $160.87   4.586%   $168.2475   $168.25   $168.25   $168.20  
  Purchase #6 $186.70   13.354%   $211.6319   $211.63   $211.65   $211.60  
  Purchase #7 $208.74   12.691%   $235.2312   $235.23   $235.25   $235.20  
  7 purchase totals = $1,030.99       $1,124.3378   $1,124.34   $1,124.40   $1,124.30