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	$154.43	10.321%	$170.3687	$170.37	$170.35	$170.40
Purchase #2	$148.95	11.629%	$166.2714	$166.27	$166.25	$166.30
Purchase #3	$244.70	8.286%	$264.9758	$264.98	$265.00	$265.00
Purchase #4	$79.73	3.189%	$82.2726	$82.27	$82.25	$82.30
Purchase #5	$48.66	12.726%	$54.8525	$54.85	$54.85	$54.90
Purchase #6	$246.99	11.427%	$275.2135	$275.21	$275.20	$275.20
Purchase #7	$128.77	10.236%	$141.9509	$141.95	$141.95	$142.00
7 purchase totals =	$1,052.23		$1,155.9054	$1,155.90	$1,155.85	$1,156.10