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	$47.38	12.216%	$53.1679	$53.17	$53.15	$53.20
Purchase #2	$243.81	10.549%	$269.5295	$269.53	$269.55	$269.50
Purchase #3	$137.41	3.306%	$141.9528	$141.95	$141.95	$142.00
Purchase #4	$25.82	6.151%	$27.4082	$27.41	$27.40	$27.40
Purchase #5	$230.43	11.495%	$256.9179	$256.92	$256.90	$256.90
Purchase #6	$64.84	4.499%	$67.7572	$67.76	$67.75	$67.80
Purchase #7	$38.31	11.363%	$42.6632	$42.66	$42.65	$42.70
7 purchase totals =	$788.00		$859.3967	$859.40	$859.35	$859.50