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	$80.38	6.128%	$85.3057	$85.31	$85.30	$85.30
Purchase #2	$220.45	6.446%	$234.6602	$234.66	$234.65	$234.70
Purchase #3	$179.95	11.262%	$200.216	$200.22	$200.20	$200.20
Purchase #4	$46.44	3.487%	$48.0594	$48.06	$48.05	$48.10
Purchase #5	$79.84	4.451%	$83.3937	$83.39	$83.40	$83.40
Purchase #6	$181.90	8.871%	$198.0363	$198.04	$198.05	$198.00
Purchase #7	$250.79	3.629%	$259.8912	$259.89	$259.90	$259.90
7 purchase totals =	$1,039.75		$1,109.5625	$1,109.57	$1,109.55	$1,109.60