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	$110.94	11.317%	$123.4951	$123.50	$123.50	$123.50
Purchase #2	$113.72	12.763%	$128.2341	$128.23	$128.25	$128.20
Purchase #3	$11.85	9.275%	$12.9491	$12.95	$12.95	$12.90
Purchase #4	$157.82	4.142%	$164.3569	$164.36	$164.35	$164.40
Purchase #5	$68.74	6.260%	$73.0431	$73.04	$73.05	$73.00
Purchase #6	$225.31	6.623%	$240.2323	$240.23	$240.25	$240.20
Purchase #7	$20.76	10.326%	$22.9037	$22.90	$22.90	$22.90
7 purchase totals =	$709.14		$765.2143	$765.21	$765.25	$765.10