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	$156.86	5.840%	$166.0206	$166.02	$166.00	$166.00
Purchase #2	$133.54	10.666%	$147.7834	$147.78	$147.80	$147.80
Purchase #3	$106.89	10.494%	$118.107	$118.11	$118.10	$118.10
Purchase #4	$119.33	8.840%	$129.8788	$129.88	$129.90	$129.90
Purchase #5	$189.43	3.494%	$196.0487	$196.05	$196.05	$196.00
Purchase #6	$119.71	6.320%	$127.2757	$127.28	$127.30	$127.30
Purchase #7	$111.88	4.333%	$116.7278	$116.73	$116.75	$116.70
7 purchase totals =	$937.64		$1,001.8420	$1,001.85	$1,001.90	$1,001.80