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	$168.80	12.605%	$190.0772	$190.08	$190.10	$190.10
Purchase #2	$26.89	8.141%	$29.0791	$29.08	$29.10	$29.10
Purchase #3	$59.77	13.160%	$67.6357	$67.64	$67.65	$67.60
Purchase #4	$56.94	4.862%	$59.7084	$59.71	$59.70	$59.70
Purchase #5	$9.25	5.227%	$9.7335	$9.73	$9.75	$9.70
Purchase #6	$78.86	10.220%	$86.9195	$86.92	$86.90	$86.90
Purchase #7	$91.56	9.114%	$99.9048	$99.90	$99.90	$99.90
7 purchase totals =	$492.07		$543.0582	$543.06	$543.10	$543.00