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	$24.58	9.794%	$26.9874	$26.99	$27.00	$27.00
Purchase #2	$125.84	4.309%	$131.2624	$131.26	$131.25	$131.30
Purchase #3	$119.96	9.112%	$130.8908	$130.89	$130.90	$130.90
Purchase #4	$228.56	4.514%	$238.8772	$238.88	$238.90	$238.90
Purchase #5	$43.72	5.119%	$45.958	$45.96	$45.95	$46.00
Purchase #6	$6.39	12.108%	$7.1637	$7.16	$7.15	$7.20
Purchase #7	$131.34	4.604%	$137.3869	$137.39	$137.40	$137.40
7 purchase totals =	$680.39		$718.5264	$718.53	$718.55	$718.70