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 $208.92   13.706%   $237.5546   $237.55   $237.55   $237.60  
  Purchase #2 $31.89   7.437%   $34.2617   $34.26   $34.25   $34.30  
  Purchase #3 $79.83   5.619%   $84.3156   $84.32   $84.30   $84.30  
  Purchase #4 $114.75   13.746%   $130.5235   $130.52   $130.50   $130.50  
  Purchase #5 $194.49   6.431%   $206.9977   $207.00   $207.00   $207.00  
  Purchase #6 $218.72   10.216%   $241.0644   $241.06   $241.05   $241.10  
  Purchase #7 $119.74   12.598%   $134.8248   $134.82   $134.80   $134.80  
  7 purchase totals = $968.34       $1,069.5423   $1,069.53   $1,069.45   $1,069.60