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 $66.27   10.246%   $73.06   $73.06   $73.05   $73.10  
  Purchase #2 $41.44   4.573%   $43.3351   $43.34   $43.35   $43.30  
  Purchase #3 $160.88   3.673%   $166.7891   $166.79   $166.80   $166.80  
  Purchase #4 $238.97   10.301%   $263.5863   $263.59   $263.60   $263.60  
  Purchase #5 $24.39   13.176%   $27.6036   $27.60   $27.60   $27.60  
  Purchase #6 $239.84   9.234%   $261.9868   $261.99   $262.00   $262.00  
  Purchase #7 $240.89   8.847%   $262.2015   $262.20   $262.20   $262.20  
  7 purchase totals = $1,012.68       $1,098.5624   $1,098.57   $1,098.60   $1,098.60