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	$104.55	10.316%	$115.3354	$115.34	$115.35	$115.30
Purchase #2	$71.64	8.821%	$77.9594	$77.96	$77.95	$78.00
Purchase #3	$155.77	11.644%	$173.9079	$173.91	$173.90	$173.90
Purchase #4	$239.62	11.679%	$267.6052	$267.61	$267.60	$267.60
Purchase #5	$168.37	10.307%	$185.7239	$185.72	$185.70	$185.70
Purchase #6	$78.98	8.801%	$85.931	$85.93	$85.95	$85.90
Purchase #7	$93.52	5.512%	$98.6748	$98.67	$98.65	$98.70
7 purchase totals =	$912.45		$1,005.1376	$1,005.14	$1,005.10	$1,005.10