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 $233.53   6.108%   $247.794   $247.79   $247.80   $247.80  
  Purchase #2 $90.88   12.455%   $102.1991   $102.20   $102.20   $102.20  
  Purchase #3 $96.45   7.398%   $103.5854   $103.59   $103.60   $103.60  
  Purchase #4 $49.93   12.209%   $56.026   $56.03   $56.05   $56.00  
  Purchase #5 $151.60   8.452%   $164.4132   $164.41   $164.40   $164.40  
  Purchase #6 $27.50   7.854%   $29.6599   $29.66   $29.65   $29.70  
  Purchase #7 $231.66   6.305%   $246.2662   $246.27   $246.25   $246.30  
  7 purchase totals = $881.55       $949.9438   $949.95   $949.95   $950.00