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 $193.28   12.523%   $217.4845   $217.48   $217.50   $217.50  
  Purchase #2 $141.80   9.356%   $155.0668   $155.07   $155.05   $155.10  
  Purchase #3 $54.44   6.328%   $57.885   $57.89   $57.90   $57.90  
  Purchase #4 $125.37   11.379%   $139.6359   $139.64   $139.65   $139.60  
  Purchase #5 $199.62   4.382%   $208.3673   $208.37   $208.35   $208.40  
  Purchase #6 $142.73   4.434%   $149.0586   $149.06   $149.05   $149.10  
  Purchase #7 $127.50   4.375%   $133.0781   $133.08   $133.10   $133.10  
  7 purchase totals = $984.74       $1,060.5762   $1,060.59   $1,060.60   $1,060.70