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	$166.70	4.385%	$174.0098	$174.01	$174.00	$174.00
Purchase #2	$129.73	11.402%	$144.5218	$144.52	$144.50	$144.50
Purchase #3	$166.45	13.482%	$188.8908	$188.89	$188.90	$188.90
Purchase #4	$173.46	8.836%	$188.7869	$188.79	$188.80	$188.80
Purchase #5	$24.42	12.607%	$27.4986	$27.50	$27.50	$27.50
Purchase #6	$184.88	13.226%	$209.3322	$209.33	$209.35	$209.30
Purchase #7	$65.87	4.797%	$69.0298	$69.03	$69.05	$69.00
7 purchase totals =	$911.51		$1,002.0699	$1,002.07	$1,002.10	$1,002.00