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	$44.30	6.789%	$47.3075	$47.31	$47.30	$47.30
Purchase #2	$166.78	13.384%	$189.1018	$189.10	$189.10	$189.10
Purchase #3	$46.27	8.762%	$50.3242	$50.32	$50.30	$50.30
Purchase #4	$208.27	5.573%	$219.8769	$219.88	$219.90	$219.90
Purchase #5	$53.55	10.472%	$59.1578	$59.16	$59.15	$59.20
Purchase #6	$166.84	13.712%	$189.7171	$189.72	$189.70	$189.70
Purchase #7	$61.86	6.325%	$65.7726	$65.77	$65.75	$65.80
7 purchase totals =	$747.87		$821.2579	$821.26	$821.20	$821.30