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	$71.66	8.573%	$77.8034	$77.80	$77.80	$77.80
Purchase #2	$187.87	6.163%	$199.4484	$199.45	$199.45	$199.40
Purchase #3	$23.33	4.204%	$24.3108	$24.31	$24.30	$24.30
Purchase #4	$156.67	11.604%	$174.85	$174.85	$174.85	$174.90
Purchase #5	$54.25	4.352%	$56.611	$56.61	$56.60	$56.60
Purchase #6	$250.41	7.751%	$269.8193	$269.82	$269.80	$269.80
Purchase #7	$44.54	8.823%	$48.4698	$48.47	$48.45	$48.50
7 purchase totals =	$788.73		$851.3127	$851.31	$851.25	$851.30