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	$81.36	4.367%	$84.913	$84.91	$84.90	$84.90
Purchase #2	$178.54	10.301%	$196.9314	$196.93	$196.95	$196.90
Purchase #3	$21.60	13.843%	$24.5901	$24.59	$24.60	$24.60
Purchase #4	$135.89	9.305%	$148.5346	$148.53	$148.55	$148.50
Purchase #5	$22.63	6.554%	$24.1132	$24.11	$24.10	$24.10
Purchase #6	$33.38	3.131%	$34.4251	$34.43	$34.45	$34.40
Purchase #7	$81.92	9.571%	$89.7606	$89.76	$89.75	$89.80
7 purchase totals =	$555.32		$603.2680	$603.26	$603.30	$603.20