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	$169.82	12.398%	$190.8743	$190.87	$190.85	$190.90
Purchase #2	$100.86	7.233%	$108.1552	$108.16	$108.15	$108.20
Purchase #3	$129.26	9.179%	$141.1248	$141.12	$141.10	$141.10
Purchase #4	$117.27	11.478%	$130.7303	$130.73	$130.75	$130.70
Purchase #5	$53.44	6.850%	$57.1006	$57.10	$57.10	$57.10
Purchase #6	$35.71	12.515%	$40.1791	$40.18	$40.20	$40.20
Purchase #7	$104.77	11.278%	$116.586	$116.59	$116.60	$116.60
7 purchase totals =	$711.13		$784.7503	$784.75	$784.75	$784.80