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	$94.89	13.263%	$107.4753	$107.48	$107.50	$107.50
Purchase #2	$190.64	6.781%	$203.5673	$203.57	$203.55	$203.60
Purchase #3	$53.31	12.361%	$59.8996	$59.90	$59.90	$59.90
Purchase #4	$37.89	7.306%	$40.6582	$40.66	$40.65	$40.70
Purchase #5	$46.60	10.735%	$51.6025	$51.60	$51.60	$51.60
Purchase #6	$12.80	6.791%	$13.6692	$13.67	$13.65	$13.70
Purchase #7	$17.85	13.777%	$20.3092	$20.31	$20.30	$20.30
7 purchase totals =	$453.98		$497.1813	$497.19	$497.15	$497.30