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	$32.28	3.830%	$33.5163	$33.52	$33.50	$33.50
Purchase #2	$47.76	8.320%	$51.7336	$51.73	$51.75	$51.70
Purchase #3	$202.52	4.248%	$211.123	$211.12	$211.10	$211.10
Purchase #4	$100.35	12.442%	$112.8355	$112.84	$112.85	$112.80
Purchase #5	$33.79	12.206%	$37.9144	$37.91	$37.90	$37.90
Purchase #6	$202.87	3.448%	$209.865	$209.87	$209.85	$209.90
Purchase #7	$177.46	6.762%	$189.4598	$189.46	$189.45	$189.50
7 purchase totals =	$797.03		$846.4476	$846.45	$846.40	$846.40