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	$133.92	8.346%	$145.097	$145.10	$145.10	$145.10
Purchase #2	$57.76	3.695%	$59.8942	$59.89	$59.90	$59.90
Purchase #3	$68.93	5.873%	$72.9783	$72.98	$73.00	$73.00
Purchase #4	$21.40	3.305%	$22.1073	$22.11	$22.10	$22.10
Purchase #5	$112.42	10.666%	$124.4107	$124.41	$124.40	$124.40
Purchase #6	$40.51	13.253%	$45.8788	$45.88	$45.90	$45.90
Purchase #7	$131.83	6.221%	$140.0311	$140.03	$140.05	$140.00
7 purchase totals =	$566.77		$610.3974	$610.40	$610.45	$610.40