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	$81.78	10.864%	$90.6646	$90.66	$90.65	$90.70
Purchase #2	$158.30	5.460%	$166.9432	$166.94	$166.95	$166.90
Purchase #3	$203.81	3.752%	$211.457	$211.46	$211.45	$211.50
Purchase #4	$135.27	5.485%	$142.6896	$142.69	$142.70	$142.70
Purchase #5	$130.89	9.335%	$143.1086	$143.11	$143.10	$143.10
Purchase #6	$241.90	11.784%	$270.4055	$270.41	$270.40	$270.40
Purchase #7	$31.58	12.609%	$35.5619	$35.56	$35.55	$35.60
7 purchase totals =	$983.53		$1,060.8304	$1,060.83	$1,060.80	$1,060.90