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 $120.69   5.207%   $126.9743   $126.97   $126.95   $127.00  
  Purchase #2 $208.59   13.354%   $236.4451   $236.45   $236.45   $236.40  
  Purchase #3 $155.80   8.113%   $168.4401   $168.44   $168.45   $168.40  
  Purchase #4 $163.27   9.166%   $178.2353   $178.24   $178.25   $178.20  
  Purchase #5 $220.79   5.523%   $232.9842   $232.98   $233.00   $233.00  
  Purchase #6 $8.78   12.651%   $9.8908   $9.89   $9.90   $9.90  
  Purchase #7 $120.72   13.417%   $136.917   $136.92   $136.90   $136.90  
  7 purchase totals = $998.64       $1,089.8868   $1,089.89   $1,089.90   $1,089.80