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	$142.90	13.865%	$162.7131	$162.71	$162.70	$162.70
Purchase #2	$223.78	7.434%	$240.4158	$240.42	$240.40	$240.40
Purchase #3	$75.76	5.810%	$80.1617	$80.16	$80.15	$80.20
Purchase #4	$39.27	9.299%	$42.9217	$42.92	$42.90	$42.90
Purchase #5	$221.35	3.670%	$229.4735	$229.47	$229.45	$229.50
Purchase #6	$187.80	12.638%	$211.5342	$211.53	$211.55	$211.50
Purchase #7	$106.52	13.455%	$120.8523	$120.85	$120.85	$120.90
7 purchase totals =	$997.38		$1,088.0723	$1,088.06	$1,088.00	$1,088.10