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	$24.93	11.112%	$27.7002	$27.70	$27.70	$27.70
Purchase #2	$49.70	13.829%	$56.573	$56.57	$56.55	$56.60
Purchase #3	$199.65	11.254%	$222.1186	$222.12	$222.10	$222.10
Purchase #4	$202.74	6.483%	$215.8836	$215.88	$215.90	$215.90
Purchase #5	$71.42	10.504%	$78.922	$78.92	$78.90	$78.90
Purchase #6	$93.33	5.843%	$98.7833	$98.78	$98.80	$98.80
Purchase #7	$5.72	6.348%	$6.0831	$6.08	$6.10	$6.10
7 purchase totals =	$647.49		$706.0638	$706.05	$706.05	$706.10