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	$6.77	13.113%	$7.6578	$7.66	$7.65	$7.70
Purchase #2	$70.93	10.370%	$78.2854	$78.29	$78.30	$78.30
Purchase #3	$126.68	5.751%	$133.9654	$133.97	$133.95	$134.00
Purchase #4	$195.89	6.767%	$209.1459	$209.15	$209.15	$209.10
Purchase #5	$99.25	12.653%	$111.8081	$111.81	$111.80	$111.80
Purchase #6	$167.35	10.636%	$185.1493	$185.15	$185.15	$185.10
Purchase #7	$194.91	9.492%	$213.4109	$213.41	$213.40	$213.40
7 purchase totals =	$861.78		$939.4228	$939.44	$939.40	$939.40