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 $142.40   10.300%   $157.0672   $157.07   $157.05   $157.10  
  Purchase #2 $13.72   10.222%   $15.1225   $15.12   $15.10   $15.10  
  Purchase #3 $93.67   6.212%   $99.4888   $99.49   $99.50   $99.50  
  Purchase #4 $227.70   12.581%   $256.3469   $256.35   $256.35   $256.30  
  Purchase #5 $174.77   10.345%   $192.85   $192.85   $192.85   $192.90  
  Purchase #6 $122.63   6.322%   $130.3827   $130.38   $130.40   $130.40  
  Purchase #7 $76.90   3.639%   $79.6984   $79.70   $79.70   $79.70  
  7 purchase totals = $851.79       $930.9565   $930.96   $930.95   $931.00