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	$61.74	8.752%	$67.1435	$67.14	$67.15	$67.10
Purchase #2	$92.56	13.746%	$105.2833	$105.28	$105.30	$105.30
Purchase #3	$135.37	9.103%	$147.6927	$147.69	$147.70	$147.70
Purchase #4	$110.34	3.736%	$114.4623	$114.46	$114.45	$114.50
Purchase #5	$33.82	13.339%	$38.3312	$38.33	$38.35	$38.30
Purchase #6	$97.49	12.366%	$109.5456	$109.55	$109.55	$109.50
Purchase #7	$76.83	5.484%	$81.0434	$81.04	$81.05	$81.00
7 purchase totals =	$608.15		$663.5020	$663.49	$663.55	$663.40