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	$116.97	10.150%	$128.8425	$128.84	$128.85	$128.80
Purchase #2	$156.62	3.512%	$162.1205	$162.12	$162.10	$162.10
Purchase #3	$183.98	13.787%	$209.3453	$209.35	$209.35	$209.30
Purchase #4	$51.89	10.530%	$57.354	$57.35	$57.35	$57.40
Purchase #5	$182.36	9.386%	$199.4763	$199.48	$199.50	$199.50
Purchase #6	$92.58	8.280%	$100.2456	$100.25	$100.25	$100.20
Purchase #7	$105.62	6.860%	$112.8655	$112.87	$112.85	$112.90
7 purchase totals =	$890.02		$970.2497	$970.26	$970.25	$970.20