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	$71.61	11.399%	$79.7728	$79.77	$79.75	$79.80
Purchase #2	$7.26	13.384%	$8.2317	$8.23	$8.25	$8.20
Purchase #3	$52.78	12.608%	$59.4345	$59.43	$59.45	$59.40
Purchase #4	$243.97	8.512%	$264.7367	$264.74	$264.75	$264.70
Purchase #5	$57.94	4.434%	$60.5091	$60.51	$60.50	$60.50
Purchase #6	$57.35	11.317%	$63.8403	$63.84	$63.85	$63.80
Purchase #7	$57.98	6.725%	$61.8792	$61.88	$61.90	$61.90
7 purchase totals =	$548.89		$598.4043	$598.40	$598.45	$598.30