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	$239.63	12.646%	$269.9336	$269.93	$269.95	$269.90
Purchase #2	$196.84	13.138%	$222.7008	$222.70	$222.70	$222.70
Purchase #3	$159.60	3.360%	$164.9626	$164.96	$164.95	$165.00
Purchase #4	$155.34	10.287%	$171.3198	$171.32	$171.30	$171.30
Purchase #5	$85.65	6.796%	$91.4708	$91.47	$91.45	$91.50
Purchase #6	$68.59	6.846%	$73.2857	$73.29	$73.30	$73.30
Purchase #7	$80.48	6.337%	$85.58	$85.58	$85.60	$85.60
7 purchase totals =	$986.13		$1,079.2533	$1,079.25	$1,079.25	$1,079.30