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	$72.51	6.334%	$77.1028	$77.10	$77.10	$77.10
Purchase #2	$84.85	9.133%	$92.5994	$92.60	$92.60	$92.60
Purchase #3	$96.58	11.709%	$107.8886	$107.89	$107.90	$107.90
Purchase #4	$249.56	12.406%	$280.5204	$280.52	$280.50	$280.50
Purchase #5	$242.92	5.708%	$256.7859	$256.79	$256.80	$256.80
Purchase #6	$93.80	11.345%	$104.4416	$104.44	$104.45	$104.40
Purchase #7	$175.95	11.388%	$195.9872	$195.99	$196.00	$196.00
7 purchase totals =	$1,016.17		$1,115.3259	$1,115.33	$1,115.35	$1,115.30