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	$159.54	13.257%	$180.6902	$180.69	$180.70	$180.70
Purchase #2	$231.70	13.872%	$263.8414	$263.84	$263.85	$263.80
Purchase #3	$176.59	6.616%	$188.2732	$188.27	$188.25	$188.30
Purchase #4	$22.26	13.841%	$25.341	$25.34	$25.35	$25.30
Purchase #5	$89.49	7.728%	$96.4058	$96.41	$96.40	$96.40
Purchase #6	$59.86	9.581%	$65.5952	$65.60	$65.60	$65.60
Purchase #7	$55.47	10.422%	$61.2511	$61.25	$61.25	$61.30
7 purchase totals =	$794.91		$881.3979	$881.40	$881.40	$881.40