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 $232.66   12.759%   $262.3451   $262.35   $262.35   $262.30  
  Purchase #2 $115.72   13.720%   $131.5968   $131.60   $131.60   $131.60  
  Purchase #3 $25.92   6.439%   $27.589   $27.59   $27.60   $27.60  
  Purchase #4 $40.76   4.212%   $42.4768   $42.48   $42.50   $42.50  
  Purchase #5 $86.64   6.207%   $92.0177   $92.02   $92.00   $92.00  
  Purchase #6 $120.28   3.362%   $124.3238   $124.32   $124.30   $124.30  
  Purchase #7 $244.74   9.368%   $267.6672   $267.67   $267.65   $267.70  
  7 purchase totals = $866.72       $948.0164   $948.03   $948.00   $948.00