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	$13.89	11.325%	$15.463	$15.46	$15.45	$15.50
Purchase #2	$166.59	11.362%	$185.518	$185.52	$185.50	$185.50
Purchase #3	$80.81	7.263%	$86.6792	$86.68	$86.70	$86.70
Purchase #4	$24.32	11.146%	$27.0307	$27.03	$27.05	$27.00
Purchase #5	$68.39	4.547%	$71.4997	$71.50	$71.50	$71.50
Purchase #6	$10.57	11.498%	$11.7853	$11.79	$11.80	$11.80
Purchase #7	$245.86	10.780%	$272.3637	$272.36	$272.35	$272.40
7 purchase totals =	$610.43		$670.3396	$670.34	$670.35	$670.40