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	$30.83	5.694%	$32.5855	$32.59	$32.60	$32.60
Purchase #2	$118.48	5.776%	$125.3234	$125.32	$125.30	$125.30
Purchase #3	$105.55	7.840%	$113.8251	$113.83	$113.85	$113.80
Purchase #4	$159.39	11.128%	$177.1269	$177.13	$177.15	$177.10
Purchase #5	$146.61	4.236%	$152.8204	$152.82	$152.80	$152.80
Purchase #6	$79.71	8.842%	$86.758	$86.76	$86.75	$86.80
Purchase #7	$146.30	4.487%	$152.8645	$152.86	$152.85	$152.90
7 purchase totals =	$786.87		$841.3038	$841.31	$841.30	$841.30