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	$36.46	8.348%	$39.5037	$39.50	$39.50	$39.50
Purchase #2	$141.44	4.856%	$148.3083	$148.31	$148.30	$148.30
Purchase #3	$175.28	8.685%	$190.5031	$190.50	$190.50	$190.50
Purchase #4	$182.70	5.361%	$192.4945	$192.49	$192.50	$192.50
Purchase #5	$225.36	12.861%	$254.3435	$254.34	$254.35	$254.30
Purchase #6	$71.92	9.682%	$78.8833	$78.88	$78.90	$78.90
Purchase #7	$185.39	6.242%	$196.962	$196.96	$196.95	$197.00
7 purchase totals =	$1,018.55		$1,100.9984	$1,100.98	$1,101.00	$1,101.00