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	$91.91	12.658%	$103.544	$103.54	$103.55	$103.50
Purchase #2	$38.69	12.824%	$43.6516	$43.65	$43.65	$43.70
Purchase #3	$27.89	9.517%	$30.5443	$30.54	$30.55	$30.50
Purchase #4	$124.53	5.629%	$131.5398	$131.54	$131.55	$131.50
Purchase #5	$203.49	10.260%	$224.3681	$224.37	$224.35	$224.40
Purchase #6	$149.50	11.309%	$166.407	$166.41	$166.40	$166.40
Purchase #7	$221.59	3.717%	$229.8265	$229.83	$229.85	$229.80
7 purchase totals =	$857.60		$929.8813	$929.88	$929.90	$929.80