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	$76.76	8.749%	$83.4757	$83.48	$83.50	$83.50
Purchase #2	$118.58	10.232%	$130.7131	$130.71	$130.70	$130.70
Purchase #3	$242.25	11.617%	$270.3922	$270.39	$270.40	$270.40
Purchase #4	$219.43	4.379%	$229.0388	$229.04	$229.05	$229.00
Purchase #5	$79.79	7.128%	$85.4774	$85.48	$85.50	$85.50
Purchase #6	$245.28	10.598%	$271.2748	$271.27	$271.25	$271.30
Purchase #7	$25.69	8.446%	$27.8598	$27.86	$27.85	$27.90
7 purchase totals =	$1,007.78		$1,098.2318	$1,098.23	$1,098.25	$1,098.30