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	$79.65	12.462%	$89.576	$89.58	$89.60	$89.60
Purchase #2	$128.37	4.597%	$134.2712	$134.27	$134.25	$134.30
Purchase #3	$199.58	12.782%	$225.0903	$225.09	$225.10	$225.10
Purchase #4	$179.89	10.642%	$199.0339	$199.03	$199.05	$199.00
Purchase #5	$47.86	13.666%	$54.4005	$54.40	$54.40	$54.40
Purchase #6	$224.43	13.574%	$254.8941	$254.89	$254.90	$254.90
Purchase #7	$70.56	6.428%	$75.0956	$75.10	$75.10	$75.10
7 purchase totals =	$930.34		$1,032.3616	$1,032.36	$1,032.40	$1,032.40