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	$77.38	6.219%	$82.1923	$82.19	$82.20	$82.20
Purchase #2	$124.85	7.193%	$133.8305	$133.83	$133.85	$133.80
Purchase #3	$185.42	8.224%	$200.6689	$200.67	$200.65	$200.70
Purchase #4	$143.96	4.519%	$150.4656	$150.47	$150.45	$150.50
Purchase #5	$91.80	3.682%	$95.1801	$95.18	$95.20	$95.20
Purchase #6	$104.61	6.677%	$111.5948	$111.59	$111.60	$111.60
Purchase #7	$235.36	12.210%	$264.0975	$264.10	$264.10	$264.10
7 purchase totals =	$963.38		$1,038.0297	$1,038.03	$1,038.05	$1,038.10