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	$79.28	13.398%	$89.9019	$89.90	$89.90	$89.90
Purchase #2	$34.65	10.473%	$38.2789	$38.28	$38.30	$38.30
Purchase #3	$193.98	5.373%	$204.4025	$204.40	$204.40	$204.40
Purchase #4	$198.79	12.447%	$223.5334	$223.53	$223.55	$223.50
Purchase #5	$88.37	12.716%	$99.6071	$99.61	$99.60	$99.60
Purchase #6	$170.57	8.495%	$185.0599	$185.06	$185.05	$185.10
Purchase #7	$184.47	8.544%	$200.2311	$200.23	$200.25	$200.20
7 purchase totals =	$950.11		$1,041.0148	$1,041.01	$1,041.05	$1,041.00