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 $212.42   12.815%   $239.6416   $239.64   $239.65   $239.60  
  Purchase #2 $21.31   13.792%   $24.2491   $24.25   $24.25   $24.20  
  Purchase #3 $187.61   3.805%   $194.7486   $194.75   $194.75   $194.70  
  Purchase #4 $178.67   10.434%   $197.3124   $197.31   $197.30   $197.30  
  Purchase #5 $249.51   7.249%   $267.597   $267.60   $267.60   $267.60  
  Purchase #6 $41.62   12.641%   $46.8812   $46.88   $46.90   $46.90  
  Purchase #7 $49.94   5.703%   $52.7881   $52.79   $52.80   $52.80  
  7 purchase totals = $941.08       $1,023.2180   $1,023.22   $1,023.25   $1,023.10