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	$47.50	5.717%	$50.2156	$50.22	$50.20	$50.20
Purchase #2	$7.45	4.846%	$7.811	$7.81	$7.80	$7.80
Purchase #3	$72.40	13.870%	$82.4419	$82.44	$82.45	$82.40
Purchase #4	$150.45	12.567%	$169.3571	$169.36	$169.35	$169.40
Purchase #5	$17.36	5.763%	$18.3605	$18.36	$18.35	$18.40
Purchase #6	$36.62	7.522%	$39.3746	$39.37	$39.35	$39.40
Purchase #7	$37.47	4.113%	$39.0111	$39.01	$39.00	$39.00
7 purchase totals =	$369.25		$406.5718	$406.57	$406.50	$406.60