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	$73.82	9.156%	$80.579	$80.58	$80.60	$80.60
Purchase #2	$119.34	5.627%	$126.0553	$126.06	$126.05	$126.10
Purchase #3	$80.75	10.706%	$89.3951	$89.40	$89.40	$89.40
Purchase #4	$124.38	7.499%	$133.7073	$133.71	$133.70	$133.70
Purchase #5	$100.99	5.399%	$106.4425	$106.44	$106.45	$106.40
Purchase #6	$144.65	6.850%	$154.5585	$154.56	$154.55	$154.60
Purchase #7	$138.43	4.126%	$144.1416	$144.14	$144.15	$144.10
7 purchase totals =	$782.36		$834.8793	$834.89	$834.90	$834.90