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	$47.53	10.574%	$52.5558	$52.56	$52.55	$52.60
Purchase #2	$27.67	10.342%	$30.5316	$30.53	$30.55	$30.50
Purchase #3	$144.85	12.485%	$162.9345	$162.93	$162.95	$162.90
Purchase #4	$29.73	8.712%	$32.3201	$32.32	$32.30	$32.30
Purchase #5	$30.99	4.511%	$32.388	$32.39	$32.40	$32.40
Purchase #6	$81.71	9.171%	$89.2036	$89.20	$89.20	$89.20
Purchase #7	$210.77	5.222%	$221.7764	$221.78	$221.80	$221.80
7 purchase totals =	$573.25		$621.7100	$621.71	$621.75	$621.70