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	$120.89	6.615%	$128.8869	$128.89	$128.90	$128.90
Purchase #2	$246.27	8.144%	$266.3262	$266.33	$266.35	$266.30
Purchase #3	$38.59	8.554%	$41.891	$41.89	$41.90	$41.90
Purchase #4	$178.73	11.653%	$199.5574	$199.56	$199.55	$199.60
Purchase #5	$79.56	7.555%	$85.5708	$85.57	$85.55	$85.60
Purchase #6	$213.96	13.502%	$242.8489	$242.85	$242.85	$242.80
Purchase #7	$99.26	6.410%	$105.6226	$105.62	$105.60	$105.60
7 purchase totals =	$977.26		$1,070.7038	$1,070.71	$1,070.70	$1,070.70