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	$99.46	4.336%	$103.7726	$103.77	$103.75	$103.80
Purchase #2	$16.35	10.419%	$18.0535	$18.05	$18.05	$18.10
Purchase #3	$141.56	9.712%	$155.3083	$155.31	$155.30	$155.30
Purchase #4	$120.41	6.457%	$128.1849	$128.18	$128.20	$128.20
Purchase #5	$167.87	9.151%	$183.2318	$183.23	$183.25	$183.20
Purchase #6	$173.52	9.591%	$190.1623	$190.16	$190.15	$190.20
Purchase #7	$109.85	7.637%	$118.2392	$118.24	$118.25	$118.20
7 purchase totals =	$829.02		$896.9526	$896.94	$896.95	$897.00