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	$36.72	4.859%	$38.5042	$38.50	$38.50	$38.50
Purchase #2	$213.91	4.642%	$223.8397	$223.84	$223.85	$223.80
Purchase #3	$58.98	7.334%	$63.3056	$63.31	$63.30	$63.30
Purchase #4	$34.26	13.711%	$38.9574	$38.96	$38.95	$39.00
Purchase #5	$53.71	10.869%	$59.5477	$59.55	$59.55	$59.50
Purchase #6	$163.64	4.562%	$171.1053	$171.11	$171.10	$171.10
Purchase #7	$103.87	10.559%	$114.8376	$114.84	$114.85	$114.80
7 purchase totals =	$665.09		$710.0975	$710.11	$710.10	$710.00