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 $229.62   10.444%   $253.6015   $253.60   $253.60   $253.60  
  Purchase #2 $63.75   12.221%   $71.5409   $71.54   $71.55   $71.50  
  Purchase #3 $28.79   4.231%   $30.0081   $30.01   $30.00   $30.00  
  Purchase #4 $196.45   4.523%   $205.3354   $205.34   $205.35   $205.30  
  Purchase #5 $202.61   5.368%   $213.4861   $213.49   $213.50   $213.50  
  Purchase #6 $190.28   6.560%   $202.7624   $202.76   $202.75   $202.80  
  Purchase #7 $52.68   6.195%   $55.9435   $55.94   $55.95   $55.90  
  7 purchase totals = $964.18       $1,032.6779   $1,032.68   $1,032.70   $1,032.60