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 $248.60   8.460%   $269.6316   $269.63   $269.65   $269.60  
  Purchase #2 $186.90   13.391%   $211.9278   $211.93   $211.95   $211.90  
  Purchase #3 $127.39   9.725%   $139.7787   $139.78   $139.80   $139.80  
  Purchase #4 $126.92   3.542%   $131.4155   $131.42   $131.40   $131.40  
  Purchase #5 $143.41   12.790%   $161.7521   $161.75   $161.75   $161.80  
  Purchase #6 $205.53   12.492%   $231.2048   $231.20   $231.20   $231.20  
  Purchase #7 $181.82   10.187%   $200.342   $200.34   $200.35   $200.30  
  7 purchase totals = $1,220.57       $1,346.0525   $1,346.05   $1,346.10   $1,346.00