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	$193.28	9.844%	$212.3065	$212.31	$212.30	$212.30
Purchase #2	$215.71	11.397%	$240.2945	$240.29	$240.30	$240.30
Purchase #3	$60.90	7.480%	$65.4553	$65.46	$65.45	$65.50
Purchase #4	$62.61	5.362%	$65.9671	$65.97	$65.95	$66.00
Purchase #5	$11.44	12.154%	$12.8304	$12.83	$12.85	$12.80
Purchase #6	$92.59	7.677%	$99.6981	$99.70	$99.70	$99.70
Purchase #7	$124.96	7.161%	$133.9084	$133.91	$133.90	$133.90
7 purchase totals =	$761.49		$830.4603	$830.47	$830.45	$830.50