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	$54.44	9.342%	$59.5258	$59.53	$59.55	$59.50
Purchase #2	$29.44	7.763%	$31.7254	$31.73	$31.75	$31.70
Purchase #3	$211.39	12.840%	$238.5325	$238.53	$238.55	$238.50
Purchase #4	$250.47	10.375%	$276.4563	$276.46	$276.45	$276.50
Purchase #5	$92.53	7.504%	$99.4735	$99.47	$99.45	$99.50
Purchase #6	$34.76	10.477%	$38.4018	$38.40	$38.40	$38.40
Purchase #7	$50.45	3.352%	$52.1411	$52.14	$52.15	$52.10
7 purchase totals =	$723.48		$796.2564	$796.26	$796.30	$796.20