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	$42.76	11.134%	$47.5209	$47.52	$47.50	$47.50
Purchase #2	$110.28	6.489%	$117.4361	$117.44	$117.45	$117.40
Purchase #3	$196.78	4.501%	$205.6371	$205.64	$205.65	$205.60
Purchase #4	$155.74	4.538%	$162.8075	$162.81	$162.80	$162.80
Purchase #5	$118.27	3.584%	$122.5088	$122.51	$122.50	$122.50
Purchase #6	$27.59	13.282%	$31.2545	$31.25	$31.25	$31.30
Purchase #7	$64.44	10.634%	$71.2925	$71.29	$71.30	$71.30
7 purchase totals =	$715.86		$758.4574	$758.46	$758.45	$758.40