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 $86.79   8.243%   $93.9441   $93.94   $93.95   $93.90  
  Purchase #2 $16.47   9.740%   $18.0742   $18.07   $18.05   $18.10  
  Purchase #3 $238.70   11.267%   $265.5943   $265.59   $265.60   $265.60  
  Purchase #4 $147.47   12.544%   $165.9686   $165.97   $165.95   $166.00  
  Purchase #5 $42.35   13.260%   $47.9656   $47.97   $47.95   $48.00  
  Purchase #6 $183.59   8.339%   $198.8996   $198.90   $198.90   $198.90  
  Purchase #7 $248.84   8.291%   $269.4713   $269.47   $269.45   $269.50  
  7 purchase totals = $964.21       $1,059.9177   $1,059.91   $1,059.85   $1,060.00