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	$6.95	13.399%	$7.8812	$7.88	$7.90	$7.90
Purchase #2	$47.63	5.799%	$50.3921	$50.39	$50.40	$50.40
Purchase #3	$105.59	4.302%	$110.1325	$110.13	$110.15	$110.10
Purchase #4	$184.30	13.479%	$209.1418	$209.14	$209.15	$209.10
Purchase #5	$115.76	6.662%	$123.4719	$123.47	$123.45	$123.50
Purchase #6	$142.69	8.810%	$155.261	$155.26	$155.25	$155.30
Purchase #7	$28.70	13.813%	$32.6643	$32.66	$32.65	$32.70
7 purchase totals =	$631.62		$688.9448	$688.93	$688.95	$689.00