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	$55.74	7.421%	$59.8765	$59.88	$59.90	$59.90
Purchase #2	$180.36	6.830%	$192.6786	$192.68	$192.70	$192.70
Purchase #3	$16.62	7.663%	$17.8936	$17.89	$17.90	$17.90
Purchase #4	$24.79	10.575%	$27.4115	$27.41	$27.40	$27.40
Purchase #5	$35.89	6.726%	$38.304	$38.30	$38.30	$38.30
Purchase #6	$37.55	8.862%	$40.8777	$40.88	$40.90	$40.90
Purchase #7	$174.30	3.284%	$180.024	$180.02	$180.00	$180.00
7 purchase totals =	$525.25		$557.0659	$557.06	$557.10	$557.10