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	$54.74	12.385%	$61.5195	$61.52	$61.50	$61.50
Purchase #2	$166.86	4.745%	$174.7775	$174.78	$174.80	$174.80
Purchase #3	$39.76	6.524%	$42.3539	$42.35	$42.35	$42.40
Purchase #4	$118.67	10.586%	$131.2324	$131.23	$131.25	$131.20
Purchase #5	$58.93	10.383%	$65.0487	$65.05	$65.05	$65.00
Purchase #6	$19.86	9.778%	$21.8019	$21.80	$21.80	$21.80
Purchase #7	$7.85	13.470%	$8.9074	$8.91	$8.90	$8.90
7 purchase totals =	$466.67		$505.6413	$505.64	$505.65	$505.60