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	$14.58	6.726%	$15.5607	$15.56	$15.55	$15.60
Purchase #2	$188.35	12.507%	$211.9069	$211.91	$211.90	$211.90
Purchase #3	$55.80	6.364%	$59.3511	$59.35	$59.35	$59.40
Purchase #4	$33.65	10.219%	$37.0887	$37.09	$37.10	$37.10
Purchase #5	$6.27	3.501%	$6.4895	$6.49	$6.50	$6.50
Purchase #6	$117.45	11.297%	$130.7183	$130.72	$130.70	$130.70
Purchase #7	$126.90	12.225%	$142.4135	$142.41	$142.40	$142.40
7 purchase totals =	$543.00		$603.5287	$603.53	$603.50	$603.60