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 $147.99   5.495%   $156.1221   $156.12   $156.10   $156.10  
  Purchase #2 $134.76   12.729%   $151.9136   $151.91   $151.90   $151.90  
  Purchase #3 $25.91   6.576%   $27.6138   $27.61   $27.60   $27.60  
  Purchase #4 $71.84   6.530%   $76.5312   $76.53   $76.55   $76.50  
  Purchase #5 $221.95   13.116%   $251.061   $251.06   $251.05   $251.10  
  Purchase #6 $65.50   13.521%   $74.3563   $74.36   $74.35   $74.40  
  Purchase #7 $209.26   11.796%   $233.9443   $233.94   $233.95   $233.90  
  7 purchase totals = $877.21       $971.5423   $971.53   $971.50   $971.50