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	$151.57	13.368%	$171.8319	$171.83	$171.85	$171.80
Purchase #2	$56.85	9.122%	$62.0359	$62.04	$62.05	$62.00
Purchase #3	$225.42	6.623%	$240.3496	$240.35	$240.35	$240.30
Purchase #4	$221.67	7.580%	$238.4726	$238.47	$238.45	$238.50
Purchase #5	$68.30	6.816%	$72.9553	$72.96	$72.95	$73.00
Purchase #6	$30.58	10.240%	$33.7114	$33.71	$33.70	$33.70
Purchase #7	$170.28	4.699%	$178.2815	$178.28	$178.30	$178.30
7 purchase totals =	$924.67		$997.6382	$997.64	$997.65	$997.60