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	$39.59	6.281%	$42.0766	$42.08	$42.10	$42.10
Purchase #2	$234.28	5.685%	$247.5988	$247.60	$247.60	$247.60
Purchase #3	$148.54	11.300%	$165.325	$165.33	$165.35	$165.30
Purchase #4	$176.37	10.230%	$194.4127	$194.41	$194.40	$194.40
Purchase #5	$191.83	7.364%	$205.9564	$205.96	$205.95	$206.00
Purchase #6	$52.77	11.251%	$58.7072	$58.71	$58.70	$58.70
Purchase #7	$223.54	6.839%	$238.8279	$238.83	$238.85	$238.80
7 purchase totals =	$1,066.92		$1,152.9046	$1,152.92	$1,152.95	$1,152.90