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	$78.76	12.486%	$88.594	$88.59	$88.60	$88.60
Purchase #2	$166.33	9.216%	$181.659	$181.66	$181.65	$181.70
Purchase #3	$76.83	7.580%	$82.6537	$82.65	$82.65	$82.70
Purchase #4	$127.41	9.441%	$139.4388	$139.44	$139.45	$139.40
Purchase #5	$103.88	11.621%	$115.9519	$115.95	$115.95	$116.00
Purchase #6	$32.31	4.423%	$33.7391	$33.74	$33.75	$33.70
Purchase #7	$36.32	8.650%	$39.4617	$39.46	$39.45	$39.50
7 purchase totals =	$621.84		$681.4982	$681.49	$681.50	$681.60