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	$12.71	7.604%	$13.6765	$13.68	$13.70	$13.70
Purchase #2	$59.70	13.810%	$67.9446	$67.94	$67.95	$67.90
Purchase #3	$89.89	9.492%	$98.4224	$98.42	$98.40	$98.40
Purchase #4	$233.33	13.435%	$264.6779	$264.68	$264.70	$264.70
Purchase #5	$114.87	7.734%	$123.754	$123.75	$123.75	$123.80
Purchase #6	$247.91	11.723%	$276.9725	$276.97	$276.95	$277.00
Purchase #7	$62.31	11.542%	$69.5018	$69.50	$69.50	$69.50
7 purchase totals =	$820.72		$914.9497	$914.94	$914.95	$915.00