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	$74.74	5.486%	$78.8402	$78.84	$78.85	$78.80
Purchase #2	$73.80	10.142%	$81.2848	$81.28	$81.30	$81.30
Purchase #3	$66.80	7.374%	$71.7258	$71.73	$71.75	$71.70
Purchase #4	$236.90	4.729%	$248.103	$248.10	$248.10	$248.10
Purchase #5	$20.65	5.472%	$21.78	$21.78	$21.80	$21.80
Purchase #6	$169.46	13.605%	$192.515	$192.52	$192.50	$192.50
Purchase #7	$78.87	5.688%	$83.3561	$83.36	$83.35	$83.40
7 purchase totals =	$721.22		$777.6049	$777.61	$777.65	$777.60