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	$109.43	13.126%	$123.7938	$123.79	$123.80	$123.80
Purchase #2	$7.65	3.767%	$7.9382	$7.94	$7.95	$7.90
Purchase #3	$160.40	13.113%	$181.4333	$181.43	$181.45	$181.40
Purchase #4	$143.94	3.354%	$148.7677	$148.77	$148.75	$148.80
Purchase #5	$180.61	4.431%	$188.6128	$188.61	$188.60	$188.60
Purchase #6	$48.66	3.846%	$50.5315	$50.53	$50.55	$50.50
Purchase #7	$171.96	4.212%	$179.203	$179.20	$179.20	$179.20
7 purchase totals =	$822.65		$880.2803	$880.27	$880.30	$880.20