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 $226.29   3.232%   $233.6037   $233.60   $233.60   $233.60  
  Purchase #2 $92.42   3.450%   $95.6085   $95.61   $95.60   $95.60  
  Purchase #3 $212.97   6.409%   $226.6192   $226.62   $226.60   $226.60  
  Purchase #4 $65.76   8.495%   $71.3463   $71.35   $71.35   $71.30  
  Purchase #5 $42.49   6.550%   $45.2731   $45.27   $45.25   $45.30  
  Purchase #6 $164.45   3.179%   $169.6779   $169.68   $169.70   $169.70  
  Purchase #7 $201.74   13.814%   $229.6084   $229.61   $229.60   $229.60  
  7 purchase totals = $1,006.12       $1,071.7371   $1,071.74   $1,071.70   $1,071.70