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 $103.86   10.201%   $114.4548   $114.45   $114.45   $114.50  
  Purchase #2 $62.95   7.662%   $67.7732   $67.77   $67.75   $67.80  
  Purchase #3 $75.27   5.285%   $79.248   $79.25   $79.25   $79.20  
  Purchase #4 $233.96   13.475%   $265.4861   $265.49   $265.50   $265.50  
  Purchase #5 $236.97   7.224%   $254.0887   $254.09   $254.10   $254.10  
  Purchase #6 $34.90   13.518%   $39.6178   $39.62   $39.60   $39.60  
  Purchase #7 $182.32   13.524%   $206.977   $206.98   $207.00   $207.00  
  7 purchase totals = $930.23       $1,027.6456   $1,027.65   $1,027.65   $1,027.70