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 $42.44   11.269%   $47.2226   $47.22   $47.20   $47.20  
  Purchase #2 $44.28   9.115%   $48.3161   $48.32   $48.30   $48.30  
  Purchase #3 $201.86   5.407%   $212.7746   $212.77   $212.75   $212.80  
  Purchase #4 $212.34   10.815%   $235.3046   $235.30   $235.30   $235.30  
  Purchase #5 $193.71   12.179%   $217.3019   $217.30   $217.30   $217.30  
  Purchase #6 $103.62   10.405%   $114.4017   $114.40   $114.40   $114.40  
  Purchase #7 $131.78   12.247%   $147.9191   $147.92   $147.90   $147.90  
  7 purchase totals = $930.03       $1,023.2406   $1,023.23   $1,023.15   $1,023.20