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	$96.82	3.720%	$100.4217	$100.42	$100.40	$100.40
Purchase #2	$73.87	5.314%	$77.7955	$77.80	$77.80	$77.80
Purchase #3	$67.39	5.814%	$71.3081	$71.31	$71.30	$71.30
Purchase #4	$110.37	5.738%	$116.703	$116.70	$116.70	$116.70
Purchase #5	$148.70	6.806%	$158.8205	$158.82	$158.80	$158.80
Purchase #6	$70.86	3.166%	$73.1034	$73.10	$73.10	$73.10
Purchase #7	$91.59	5.473%	$96.6027	$96.60	$96.60	$96.60
7 purchase totals =	$659.60		$694.7549	$694.75	$694.70	$694.70