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 $52.92   5.844%   $56.0126   $56.01   $56.00   $56.00  
  Purchase #2 $57.96   7.460%   $62.2838   $62.28   $62.30   $62.30  
  Purchase #3 $232.70   8.164%   $251.6976   $251.70   $251.70   $251.70  
  Purchase #4 $239.95   10.536%   $265.2311   $265.23   $265.25   $265.20  
  Purchase #5 $114.86   13.130%   $129.9411   $129.94   $129.95   $129.90  
  Purchase #6 $93.28   13.210%   $105.6023   $105.60   $105.60   $105.60  
  Purchase #7 $166.98   6.142%   $177.2359   $177.24   $177.25   $177.20  
  7 purchase totals = $958.65       $1,048.0044   $1,048.00   $1,048.05   $1,047.90