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	$60.31	10.427%	$66.5985	$66.60	$66.60	$66.60
Purchase #2	$130.28	13.374%	$147.7036	$147.70	$147.70	$147.70
Purchase #3	$124.83	4.767%	$130.7806	$130.78	$130.80	$130.80
Purchase #4	$157.44	10.822%	$174.4782	$174.48	$174.50	$174.50
Purchase #5	$88.41	11.489%	$98.5674	$98.57	$98.55	$98.60
Purchase #6	$246.98	12.712%	$278.3761	$278.38	$278.40	$278.40
Purchase #7	$178.62	6.235%	$189.757	$189.76	$189.75	$189.80
7 purchase totals =	$986.87		$1,086.2614	$1,086.27	$1,086.30	$1,086.40