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 $61.35   13.166%   $69.4273   $69.43   $69.45   $69.40  
  Purchase #2 $162.28   12.493%   $182.5536   $182.55   $182.55   $182.60  
  Purchase #3 $162.30   13.326%   $183.9281   $183.93   $183.95   $183.90  
  Purchase #4 $196.98   3.615%   $204.1008   $204.10   $204.10   $204.10  
  Purchase #5 $219.77   3.201%   $226.8048   $226.80   $226.80   $226.80  
  Purchase #6 $239.98   10.507%   $265.1947   $265.19   $265.20   $265.20  
  Purchase #7 $236.38   5.407%   $249.1611   $249.16   $249.15   $249.20  
  7 purchase totals = $1,279.04       $1,381.1704   $1,381.16   $1,381.20   $1,381.20