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	$174.27	8.820%	$189.6406	$189.64	$189.65	$189.60
Purchase #2	$229.64	5.761%	$242.8696	$242.87	$242.85	$242.90
Purchase #3	$71.29	10.163%	$78.5352	$78.54	$78.55	$78.50
Purchase #4	$169.59	10.428%	$187.2748	$187.27	$187.25	$187.30
Purchase #5	$188.56	6.388%	$200.6052	$200.61	$200.60	$200.60
Purchase #6	$28.33	7.161%	$30.3587	$30.36	$30.35	$30.40
Purchase #7	$80.59	12.782%	$90.891	$90.89	$90.90	$90.90
7 purchase totals =	$942.27		$1,020.1751	$1,020.18	$1,020.15	$1,020.20