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 $60.43   13.335%   $68.4883   $68.49   $68.50   $68.50  
  Purchase #2 $167.54   10.620%   $185.3327   $185.33   $185.35   $185.30  
  Purchase #3 $159.81   9.347%   $174.7474   $174.75   $174.75   $174.70  
  Purchase #4 $71.46   13.393%   $81.0306   $81.03   $81.05   $81.00  
  Purchase #5 $178.47   10.395%   $197.022   $197.02   $197.00   $197.00  
  Purchase #6 $48.80   8.344%   $52.8719   $52.87   $52.85   $52.90  
  Purchase #7 $249.48   6.263%   $265.1049   $265.10   $265.10   $265.10  
  7 purchase totals = $935.99       $1,024.5978   $1,024.59   $1,024.60   $1,024.50