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	$50.35	6.382%	$53.5633	$53.56	$53.55	$53.60
Purchase #2	$200.33	6.778%	$213.9084	$213.91	$213.90	$213.90
Purchase #3	$77.89	9.537%	$85.3184	$85.32	$85.30	$85.30
Purchase #4	$151.49	9.791%	$166.3224	$166.32	$166.30	$166.30
Purchase #5	$249.56	10.498%	$275.7588	$275.76	$275.75	$275.80
Purchase #6	$166.68	4.365%	$173.9556	$173.96	$173.95	$174.00
Purchase #7	$47.45	7.594%	$51.0534	$51.05	$51.05	$51.10
7 purchase totals =	$943.75		$1,019.8803	$1,019.88	$1,019.80	$1,020.00