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	$151.46	12.427%	$170.2819	$170.28	$170.30	$170.30
Purchase #2	$215.89	3.570%	$223.5973	$223.60	$223.60	$223.60
Purchase #3	$67.68	3.550%	$70.0826	$70.08	$70.10	$70.10
Purchase #4	$152.64	6.714%	$162.8882	$162.89	$162.90	$162.90
Purchase #5	$183.84	13.439%	$208.5463	$208.55	$208.55	$208.50
Purchase #6	$94.85	9.145%	$103.524	$103.52	$103.50	$103.50
Purchase #7	$10.98	6.805%	$11.7272	$11.73	$11.75	$11.70
7 purchase totals =	$877.34		$950.6475	$950.65	$950.70	$950.60