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 $66.63   7.311%   $71.5013   $71.50   $71.50   $71.50  
  Purchase #2 $56.69   10.755%   $62.787   $62.79   $62.80   $62.80  
  Purchase #3 $6.30   6.187%   $6.6898   $6.69   $6.70   $6.70  
  Purchase #4 $48.84   8.364%   $52.925   $52.93   $52.95   $52.90  
  Purchase #5 $221.26   8.121%   $239.2285   $239.23   $239.25   $239.20  
  Purchase #6 $192.40   8.644%   $209.0311   $209.03   $209.05   $209.00  
  Purchase #7 $57.56   7.570%   $61.9173   $61.92   $61.90   $61.90  
  7 purchase totals = $649.68       $704.0800   $704.09   $704.15   $704.00