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	$40.98	3.863%	$42.5631	$42.56	$42.55	$42.60
Purchase #2	$40.41	9.669%	$44.3172	$44.32	$44.30	$44.30
Purchase #3	$56.91	5.282%	$59.916	$59.92	$59.90	$59.90
Purchase #4	$48.57	12.114%	$54.4538	$54.45	$54.45	$54.50
Purchase #5	$198.62	3.221%	$205.0176	$205.02	$205.00	$205.00
Purchase #6	$188.54	6.731%	$201.2306	$201.23	$201.25	$201.20
Purchase #7	$38.90	3.183%	$40.1382	$40.14	$40.15	$40.10
7 purchase totals =	$612.93		$647.6365	$647.64	$647.60	$647.60