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	$110.46	6.592%	$117.7415	$117.74	$117.75	$117.70
Purchase #2	$134.47	5.713%	$142.1523	$142.15	$142.15	$142.20
Purchase #3	$123.64	12.693%	$139.3336	$139.33	$139.35	$139.30
Purchase #4	$83.68	10.519%	$92.4823	$92.48	$92.50	$92.50
Purchase #5	$84.53	8.302%	$91.5477	$91.55	$91.55	$91.50
Purchase #6	$216.70	10.501%	$239.4557	$239.46	$239.45	$239.50
Purchase #7	$158.28	13.432%	$179.5402	$179.54	$179.55	$179.50
7 purchase totals =	$911.76		$1,002.2533	$1,002.25	$1,002.30	$1,002.20