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	$110.84	11.249%	$123.3084	$123.31	$123.30	$123.30
Purchase #2	$233.43	11.658%	$260.6433	$260.64	$260.65	$260.60
Purchase #3	$144.51	12.578%	$162.6865	$162.69	$162.70	$162.70
Purchase #4	$69.53	3.721%	$72.1172	$72.12	$72.10	$72.10
Purchase #5	$235.86	10.289%	$260.1276	$260.13	$260.15	$260.10
Purchase #6	$130.39	9.482%	$142.7536	$142.75	$142.75	$142.80
Purchase #7	$136.56	5.775%	$144.4463	$144.45	$144.45	$144.40
7 purchase totals =	$1,061.12		$1,166.0829	$1,166.09	$1,166.10	$1,166.00