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	$135.93	9.277%	$148.5402	$148.54	$148.55	$148.50
Purchase #2	$222.69	6.380%	$236.8976	$236.90	$236.90	$236.90
Purchase #3	$25.31	11.219%	$28.1495	$28.15	$28.15	$28.10
Purchase #4	$18.87	13.376%	$21.3941	$21.39	$21.40	$21.40
Purchase #5	$84.73	6.371%	$90.1281	$90.13	$90.15	$90.10
Purchase #6	$44.72	8.584%	$48.5588	$48.56	$48.55	$48.60
Purchase #7	$91.53	10.844%	$101.4555	$101.46	$101.45	$101.50
7 purchase totals =	$623.78		$675.1238	$675.13	$675.15	$675.10