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	$45.96	10.392%	$50.7362	$50.74	$50.75	$50.70
Purchase #2	$161.94	8.617%	$175.8944	$175.89	$175.90	$175.90
Purchase #3	$51.30	12.594%	$57.7607	$57.76	$57.75	$57.80
Purchase #4	$129.36	12.760%	$145.8663	$145.87	$145.85	$145.90
Purchase #5	$37.87	7.673%	$40.7758	$40.78	$40.80	$40.80
Purchase #6	$49.45	5.137%	$51.9902	$51.99	$52.00	$52.00
Purchase #7	$93.85	7.474%	$100.8643	$100.86	$100.85	$100.90
7 purchase totals =	$569.73		$623.8879	$623.89	$623.90	$624.00