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	$166.47	6.534%	$177.3471	$177.35	$177.35	$177.30
Purchase #2	$72.92	6.383%	$77.5745	$77.57	$77.55	$77.60
Purchase #3	$71.52	11.367%	$79.6497	$79.65	$79.65	$79.60
Purchase #4	$91.83	8.687%	$99.8073	$99.81	$99.80	$99.80
Purchase #5	$31.40	6.168%	$33.3368	$33.34	$33.35	$33.30
Purchase #6	$170.90	5.155%	$179.7099	$179.71	$179.70	$179.70
Purchase #7	$17.82	7.119%	$19.0886	$19.09	$19.10	$19.10
7 purchase totals =	$622.86		$666.5139	$666.52	$666.50	$666.40