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	$177.50	4.518%	$185.5195	$185.52	$185.50	$185.50
Purchase #2	$183.92	7.809%	$198.2823	$198.28	$198.30	$198.30
Purchase #3	$30.37	6.732%	$32.4145	$32.41	$32.40	$32.40
Purchase #4	$215.60	10.630%	$238.5183	$238.52	$238.50	$238.50
Purchase #5	$104.29	5.290%	$109.8069	$109.81	$109.80	$109.80
Purchase #6	$79.50	8.421%	$86.1947	$86.19	$86.20	$86.20
Purchase #7	$34.92	13.476%	$39.6258	$39.63	$39.65	$39.60
7 purchase totals =	$826.10		$890.3620	$890.36	$890.35	$890.30