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	$26.50	8.666%	$28.7965	$28.80	$28.80	$28.80
Purchase #2	$112.31	13.512%	$127.4853	$127.49	$127.50	$127.50
Purchase #3	$236.47	7.280%	$253.685	$253.69	$253.70	$253.70
Purchase #4	$127.63	10.385%	$140.8844	$140.88	$140.90	$140.90
Purchase #5	$241.48	5.794%	$255.4714	$255.47	$255.45	$255.50
Purchase #6	$81.30	13.460%	$92.243	$92.24	$92.25	$92.20
Purchase #7	$124.80	6.621%	$133.063	$133.06	$133.05	$133.10
7 purchase totals =	$950.49		$1,031.6286	$1,031.63	$1,031.65	$1,031.70