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	$92.99	7.811%	$100.2534	$100.25	$100.25	$100.30
Purchase #2	$20.27	7.848%	$21.8608	$21.86	$21.85	$21.90
Purchase #3	$173.40	10.308%	$191.2741	$191.27	$191.25	$191.30
Purchase #4	$39.98	5.157%	$42.0418	$42.04	$42.05	$42.00
Purchase #5	$6.42	12.171%	$7.2014	$7.20	$7.20	$7.20
Purchase #6	$64.76	5.614%	$68.3956	$68.40	$68.40	$68.40
Purchase #7	$227.28	3.785%	$235.8825	$235.88	$235.90	$235.90
7 purchase totals =	$625.10		$666.9096	$666.90	$666.90	$667.00