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	$84.75	6.776%	$90.4927	$90.49	$90.50	$90.50
Purchase #2	$7.78	11.424%	$8.6688	$8.67	$8.65	$8.70
Purchase #3	$56.86	8.355%	$61.6107	$61.61	$61.60	$61.60
Purchase #4	$139.76	5.541%	$147.5041	$147.50	$147.50	$147.50
Purchase #5	$48.80	11.761%	$54.5394	$54.54	$54.55	$54.50
Purchase #6	$145.40	9.271%	$158.88	$158.88	$158.90	$158.90
Purchase #7	$196.71	6.840%	$210.165	$210.17	$210.15	$210.20
7 purchase totals =	$680.06		$731.8607	$731.86	$731.85	$731.90