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	$150.37	5.652%	$158.8689	$158.87	$158.85	$158.90
Purchase #2	$94.58	9.846%	$103.8923	$103.89	$103.90	$103.90
Purchase #3	$158.99	4.695%	$166.4546	$166.45	$166.45	$166.50
Purchase #4	$96.91	6.746%	$103.4475	$103.45	$103.45	$103.40
Purchase #5	$180.64	12.754%	$203.6788	$203.68	$203.70	$203.70
Purchase #6	$215.97	6.323%	$229.6258	$229.63	$229.65	$229.60
Purchase #7	$213.57	9.228%	$233.2782	$233.28	$233.30	$233.30
7 purchase totals =	$1,111.03		$1,199.2461	$1,199.25	$1,199.30	$1,199.30