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	$155.63	8.151%	$168.3154	$168.32	$168.30	$168.30
Purchase #2	$125.50	11.173%	$139.5221	$139.52	$139.50	$139.50
Purchase #3	$46.74	5.873%	$49.485	$49.49	$49.50	$49.50
Purchase #4	$76.29	4.282%	$79.5567	$79.56	$79.55	$79.60
Purchase #5	$83.41	8.787%	$90.7392	$90.74	$90.75	$90.70
Purchase #6	$176.33	6.654%	$188.063	$188.06	$188.05	$188.10
Purchase #7	$168.51	3.601%	$174.578	$174.58	$174.60	$174.60
7 purchase totals =	$832.41		$890.2594	$890.27	$890.25	$890.30