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	$22.92	8.583%	$24.8872	$24.89	$24.90	$24.90
Purchase #2	$153.50	3.598%	$159.0229	$159.02	$159.00	$159.00
Purchase #3	$52.33	7.338%	$56.17	$56.17	$56.15	$56.20
Purchase #4	$33.43	4.534%	$34.9457	$34.95	$34.95	$34.90
Purchase #5	$100.87	4.322%	$105.2296	$105.23	$105.25	$105.20
Purchase #6	$36.41	8.874%	$39.641	$39.64	$39.65	$39.60
Purchase #7	$73.43	13.107%	$83.0545	$83.05	$83.05	$83.10
7 purchase totals =	$472.89		$502.9509	$502.95	$502.95	$502.90