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	$78.38	6.347%	$83.3548	$83.35	$83.35	$83.40
Purchase #2	$167.71	13.292%	$190.002	$190.00	$190.00	$190.00
Purchase #3	$58.92	9.458%	$64.4927	$64.49	$64.50	$64.50
Purchase #4	$14.89	9.846%	$16.3561	$16.36	$16.35	$16.40
Purchase #5	$49.74	6.103%	$52.7756	$52.78	$52.80	$52.80
Purchase #6	$249.25	6.224%	$264.7633	$264.76	$264.75	$264.80
Purchase #7	$36.55	10.546%	$40.4046	$40.40	$40.40	$40.40
7 purchase totals =	$655.44		$712.1491	$712.14	$712.15	$712.30