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	$24.48	13.416%	$27.7642	$27.76	$27.75	$27.80
Purchase #2	$52.77	10.820%	$58.4797	$58.48	$58.50	$58.50
Purchase #3	$63.27	6.746%	$67.5382	$67.54	$67.55	$67.50
Purchase #4	$21.68	3.252%	$22.385	$22.39	$22.40	$22.40
Purchase #5	$75.57	3.415%	$78.1507	$78.15	$78.15	$78.20
Purchase #6	$40.63	3.736%	$42.1479	$42.15	$42.15	$42.10
Purchase #7	$66.47	10.182%	$73.238	$73.24	$73.25	$73.20
7 purchase totals =	$344.87		$369.7037	$369.71	$369.75	$369.70