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	$64.56	8.839%	$70.2665	$70.27	$70.25	$70.30
Purchase #2	$141.49	10.493%	$156.3365	$156.34	$156.35	$156.30
Purchase #3	$194.86	9.560%	$213.4886	$213.49	$213.50	$213.50
Purchase #4	$249.97	6.302%	$265.7231	$265.72	$265.70	$265.70
Purchase #5	$111.83	4.399%	$116.7494	$116.75	$116.75	$116.70
Purchase #6	$228.39	7.680%	$245.9304	$245.93	$245.95	$245.90
Purchase #7	$155.50	6.320%	$165.3276	$165.33	$165.35	$165.30
7 purchase totals =	$1,146.60		$1,233.8221	$1,233.83	$1,233.85	$1,233.70