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	$131.75	9.174%	$143.8367	$143.84	$143.85	$143.80
Purchase #2	$234.87	6.609%	$250.3926	$250.39	$250.40	$250.40
Purchase #3	$74.48	9.849%	$81.8155	$81.82	$81.80	$81.80
Purchase #4	$118.82	9.344%	$129.9225	$129.92	$129.90	$129.90
Purchase #5	$33.70	6.352%	$35.8406	$35.84	$35.85	$35.80
Purchase #6	$172.32	13.768%	$196.045	$196.05	$196.05	$196.00
Purchase #7	$137.33	13.516%	$155.8915	$155.89	$155.90	$155.90
7 purchase totals =	$903.27		$993.7444	$993.75	$993.75	$993.60