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	$25.86	7.624%	$27.8316	$27.83	$27.85	$27.80
Purchase #2	$58.37	5.449%	$61.5506	$61.55	$61.55	$61.60
Purchase #3	$128.49	3.698%	$133.2416	$133.24	$133.25	$133.20
Purchase #4	$46.55	9.332%	$50.894	$50.89	$50.90	$50.90
Purchase #5	$183.50	7.763%	$197.7451	$197.75	$197.75	$197.70
Purchase #6	$53.54	11.557%	$59.7276	$59.73	$59.75	$59.70
Purchase #7	$73.42	6.615%	$78.2767	$78.28	$78.30	$78.30
7 purchase totals =	$569.73		$609.2672	$609.27	$609.35	$609.20