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 $208.85   12.270%   $234.4759   $234.48   $234.50   $234.50  
  Purchase #2 $109.55   9.175%   $119.6012   $119.60   $119.60   $119.60  
  Purchase #3 $213.90   4.754%   $224.0688   $224.07   $224.05   $224.10  
  Purchase #4 $44.65   12.430%   $50.2   $50.20   $50.20   $50.20  
  Purchase #5 $39.71   7.571%   $42.7164   $42.72   $42.70   $42.70  
  Purchase #6 $96.77   9.461%   $105.9254   $105.93   $105.95   $105.90  
  Purchase #7 $92.79   5.633%   $98.0169   $98.02   $98.00   $98.00  
  7 purchase totals = $806.22       $875.0046   $875.02   $875.00   $875.00