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 $197.61   5.288%   $208.0596   $208.06   $208.05   $208.10  
  Purchase #2 $129.99   10.441%   $143.5623   $143.56   $143.55   $143.60  
  Purchase #3 $244.88   13.657%   $278.3233   $278.32   $278.30   $278.30  
  Purchase #4 $60.87   7.716%   $65.5667   $65.57   $65.55   $65.60  
  Purchase #5 $130.61   6.336%   $138.8854   $138.89   $138.90   $138.90  
  Purchase #6 $218.44   11.627%   $243.838   $243.84   $243.85   $243.80  
  Purchase #7 $238.37   11.551%   $265.9041   $265.90   $265.90   $265.90  
  7 purchase totals = $1,220.77       $1,344.1394   $1,344.14   $1,344.10   $1,344.20