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	$175.37	5.715%	$185.3924	$185.39	$185.40	$185.40
Purchase #2	$10.67	10.731%	$11.815	$11.82	$11.80	$11.80
Purchase #3	$110.67	3.697%	$114.7615	$114.76	$114.75	$114.80
Purchase #4	$21.98	12.404%	$24.7064	$24.71	$24.70	$24.70
Purchase #5	$207.53	4.417%	$216.6966	$216.70	$216.70	$216.70
Purchase #6	$74.71	10.474%	$82.5351	$82.54	$82.55	$82.50
Purchase #7	$21.89	12.145%	$24.5485	$24.55	$24.55	$24.50
7 purchase totals =	$622.82		$660.4555	$660.47	$660.45	$660.40