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	$52.99	4.794%	$55.5303	$55.53	$55.55	$55.50
Purchase #2	$194.74	6.753%	$207.8908	$207.89	$207.90	$207.90
Purchase #3	$89.49	8.317%	$96.9329	$96.93	$96.95	$96.90
Purchase #4	$77.75	6.655%	$82.9243	$82.92	$82.90	$82.90
Purchase #5	$102.69	10.755%	$113.7343	$113.73	$113.75	$113.70
Purchase #6	$30.38	10.233%	$33.4888	$33.49	$33.50	$33.50
Purchase #7	$225.65	13.302%	$255.666	$255.67	$255.65	$255.70
7 purchase totals =	$773.69		$846.1674	$846.16	$846.20	$846.10