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	$129.68	9.705%	$142.2654	$142.27	$142.25	$142.30
Purchase #2	$93.91	6.344%	$99.8677	$99.87	$99.85	$99.90
Purchase #3	$184.52	5.571%	$194.7996	$194.80	$194.80	$194.80
Purchase #4	$66.74	5.225%	$70.2272	$70.23	$70.25	$70.20
Purchase #5	$67.73	6.209%	$71.9354	$71.94	$71.95	$71.90
Purchase #6	$140.92	9.325%	$154.0608	$154.06	$154.05	$154.10
Purchase #7	$82.64	3.385%	$85.4374	$85.44	$85.45	$85.40
7 purchase totals =	$766.14		$818.5935	$818.61	$818.60	$818.60