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 $44.87   11.513%   $50.0359   $50.04   $50.05   $50.00  
  Purchase #2 $114.65   8.446%   $124.3333   $124.33   $124.35   $124.30  
  Purchase #3 $217.52   12.656%   $245.0493   $245.05   $245.05   $245.00  
  Purchase #4 $221.61   9.307%   $242.2352   $242.24   $242.25   $242.20  
  Purchase #5 $228.63   10.436%   $252.4898   $252.49   $252.50   $252.50  
  Purchase #6 $97.70   13.805%   $111.1875   $111.19   $111.20   $111.20  
  Purchase #7 $152.41   3.869%   $158.3067   $158.31   $158.30   $158.30  
  7 purchase totals = $1,077.39       $1,183.6377   $1,183.65   $1,183.70   $1,183.50