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	$55.38	8.190%	$59.9156	$59.92	$59.90	$59.90
Purchase #2	$156.99	5.298%	$165.3073	$165.31	$165.30	$165.30
Purchase #3	$102.27	6.402%	$108.8173	$108.82	$108.80	$108.80
Purchase #4	$162.99	6.833%	$174.1271	$174.13	$174.15	$174.10
Purchase #5	$240.96	9.445%	$263.7187	$263.72	$263.70	$263.70
Purchase #6	$133.71	4.169%	$139.2844	$139.28	$139.30	$139.30
Purchase #7	$161.44	6.622%	$172.1306	$172.13	$172.15	$172.10
7 purchase totals =	$1,013.74		$1,083.3010	$1,083.31	$1,083.30	$1,083.20