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 $206.60   13.681%   $234.8649   $234.86   $234.85   $234.90  
  Purchase #2 $158.87   9.294%   $173.6354   $173.64   $173.65   $173.60  
  Purchase #3 $100.99   13.682%   $114.8075   $114.81   $114.80   $114.80  
  Purchase #4 $161.68   12.281%   $181.5359   $181.54   $181.55   $181.50  
  Purchase #5 $32.66   10.480%   $36.0828   $36.08   $36.10   $36.10  
  Purchase #6 $213.94   9.822%   $234.9532   $234.95   $234.95   $235.00  
  Purchase #7 $86.42   6.781%   $92.2801   $92.28   $92.30   $92.30  
  7 purchase totals = $961.16       $1,068.1598   $1,068.16   $1,068.20   $1,068.20