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	$13.39	11.413%	$14.9182	$14.92	$14.90	$14.90
Purchase #2	$143.72	7.110%	$153.9385	$153.94	$153.95	$153.90
Purchase #3	$119.71	9.822%	$131.4679	$131.47	$131.45	$131.50
Purchase #4	$122.34	6.263%	$130.0022	$130.00	$130.00	$130.00
Purchase #5	$76.25	7.577%	$82.0275	$82.03	$82.05	$82.00
Purchase #6	$147.33	4.608%	$154.119	$154.12	$154.10	$154.10
Purchase #7	$90.59	9.409%	$99.1136	$99.11	$99.10	$99.10
7 purchase totals =	$713.33		$765.5869	$765.59	$765.55	$765.50