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	$137.93	5.140%	$145.0196	$145.02	$145.00	$145.00
Purchase #2	$162.43	10.629%	$179.6947	$179.69	$179.70	$179.70
Purchase #3	$9.67	13.544%	$10.9797	$10.98	$11.00	$11.00
Purchase #4	$89.30	9.663%	$97.9291	$97.93	$97.95	$97.90
Purchase #5	$132.26	9.756%	$145.1633	$145.16	$145.15	$145.20
Purchase #6	$73.70	11.650%	$82.2861	$82.29	$82.30	$82.30
Purchase #7	$119.82	6.673%	$127.8156	$127.82	$127.80	$127.80
7 purchase totals =	$725.11		$788.8881	$788.89	$788.90	$788.90