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	$143.55	4.823%	$150.4734	$150.47	$150.45	$150.50
Purchase #2	$164.97	9.640%	$180.8731	$180.87	$180.85	$180.90
Purchase #3	$92.71	13.217%	$104.9635	$104.96	$104.95	$105.00
Purchase #4	$248.78	6.817%	$265.7393	$265.74	$265.75	$265.70
Purchase #5	$6.87	10.404%	$7.5848	$7.58	$7.60	$7.60
Purchase #6	$46.99	9.423%	$51.4179	$51.42	$51.40	$51.40
Purchase #7	$171.90	4.474%	$179.5908	$179.59	$179.60	$179.60
7 purchase totals =	$875.77		$940.6428	$940.63	$940.60	$940.70