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	$120.32	6.450%	$128.0806	$128.08	$128.10	$128.10
Purchase #2	$242.78	12.244%	$272.506	$272.51	$272.50	$272.50
Purchase #3	$67.47	5.802%	$71.3846	$71.38	$71.40	$71.40
Purchase #4	$92.59	10.312%	$102.1379	$102.14	$102.15	$102.10
Purchase #5	$44.80	7.472%	$48.1475	$48.15	$48.15	$48.10
Purchase #6	$81.73	9.752%	$89.7003	$89.70	$89.70	$89.70
Purchase #7	$78.88	11.524%	$87.9701	$87.97	$87.95	$88.00
7 purchase totals =	$728.57		$799.9270	$799.93	$799.95	$799.90