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	$145.74	9.685%	$159.8549	$159.85	$159.85	$159.90
Purchase #2	$152.88	4.242%	$159.3652	$159.37	$159.35	$159.40
Purchase #3	$129.56	5.363%	$136.5083	$136.51	$136.50	$136.50
Purchase #4	$88.45	13.653%	$100.5261	$100.53	$100.55	$100.50
Purchase #5	$98.93	3.803%	$102.6923	$102.69	$102.70	$102.70
Purchase #6	$179.31	4.745%	$187.8183	$187.82	$187.80	$187.80
Purchase #7	$79.57	4.667%	$83.2835	$83.28	$83.30	$83.30
7 purchase totals =	$874.44		$930.0486	$930.05	$930.05	$930.10