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	$80.42	12.168%	$90.2055	$90.21	$90.20	$90.20
Purchase #2	$131.27	6.654%	$140.0047	$140.00	$140.00	$140.00
Purchase #3	$66.62	3.762%	$69.1262	$69.13	$69.15	$69.10
Purchase #4	$229.36	6.526%	$244.328	$244.33	$244.35	$244.30
Purchase #5	$174.52	9.338%	$190.8167	$190.82	$190.80	$190.80
Purchase #6	$78.73	6.133%	$83.5585	$83.56	$83.55	$83.60
Purchase #7	$92.90	6.663%	$99.0899	$99.09	$99.10	$99.10
7 purchase totals =	$853.82		$917.1295	$917.14	$917.15	$917.10