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	$99.76	13.542%	$113.2695	$113.27	$113.25	$113.30
Purchase #2	$57.91	3.446%	$59.9056	$59.91	$59.90	$59.90
Purchase #3	$76.69	3.518%	$79.388	$79.39	$79.40	$79.40
Purchase #4	$246.30	8.400%	$266.9892	$266.99	$267.00	$267.00
Purchase #5	$78.33	8.201%	$84.7538	$84.75	$84.75	$84.80
Purchase #6	$162.53	6.170%	$172.5581	$172.56	$172.55	$172.60
Purchase #7	$57.96	7.718%	$62.4334	$62.43	$62.45	$62.40
7 purchase totals =	$779.48		$839.2976	$839.30	$839.30	$839.40