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	$52.28	3.349%	$54.0309	$54.03	$54.05	$54.00
Purchase #2	$99.56	6.757%	$106.2873	$106.29	$106.30	$106.30
Purchase #3	$98.27	6.284%	$104.4453	$104.45	$104.45	$104.40
Purchase #4	$232.81	7.374%	$249.9774	$249.98	$250.00	$250.00
Purchase #5	$74.73	10.496%	$82.5737	$82.57	$82.55	$82.60
Purchase #6	$151.51	12.505%	$170.4563	$170.46	$170.45	$170.50
Purchase #7	$30.36	7.263%	$32.565	$32.57	$32.55	$32.60
7 purchase totals =	$739.52		$800.3359	$800.35	$800.35	$800.40