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 $86.58   12.341%   $97.2648   $97.26   $97.25   $97.30  
  Purchase #2 $88.61   8.482%   $96.1259   $96.13   $96.15   $96.10  
  Purchase #3 $148.81   6.164%   $157.9826   $157.98   $158.00   $158.00  
  Purchase #4 $227.69   5.597%   $240.4338   $240.43   $240.45   $240.40  
  Purchase #5 $119.92   10.839%   $132.9181   $132.92   $132.90   $132.90  
  Purchase #6 $185.77   6.264%   $197.4066   $197.41   $197.40   $197.40  
  Purchase #7 $50.62   6.651%   $53.9867   $53.99   $54.00   $54.00  
  7 purchase totals = $908.00       $976.1185   $976.12   $976.15   $976.10