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	$41.40	9.644%	$45.3926	$45.39	$45.40	$45.40
Purchase #2	$79.43	9.401%	$86.8972	$86.90	$86.90	$86.90
Purchase #3	$228.48	4.231%	$238.147	$238.15	$238.15	$238.10
Purchase #4	$51.94	10.817%	$57.5583	$57.56	$57.55	$57.60
Purchase #5	$203.67	10.823%	$225.7132	$225.71	$225.70	$225.70
Purchase #6	$98.69	13.702%	$112.2125	$112.21	$112.20	$112.20
Purchase #7	$140.89	5.191%	$148.2036	$148.20	$148.20	$148.20
7 purchase totals =	$844.50		$914.1244	$914.12	$914.10	$914.10