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	$61.84	11.729%	$69.0932	$69.09	$69.10	$69.10
Purchase #2	$151.72	7.210%	$162.659	$162.66	$162.65	$162.70
Purchase #3	$79.69	3.253%	$82.2823	$82.28	$82.30	$82.30
Purchase #4	$37.64	5.668%	$39.7734	$39.77	$39.75	$39.80
Purchase #5	$178.69	5.802%	$189.0576	$189.06	$189.05	$189.10
Purchase #6	$248.25	10.704%	$274.8227	$274.82	$274.80	$274.80
Purchase #7	$228.50	13.401%	$259.1213	$259.12	$259.10	$259.10
7 purchase totals =	$986.33		$1,076.8095	$1,076.80	$1,076.75	$1,076.90