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	$150.37	10.358%	$165.9453	$165.95	$165.95	$165.90
Purchase #2	$28.37	12.857%	$32.0175	$32.02	$32.00	$32.00
Purchase #3	$49.72	5.367%	$52.3885	$52.39	$52.40	$52.40
Purchase #4	$158.34	6.632%	$168.8411	$168.84	$168.85	$168.80
Purchase #5	$49.67	9.142%	$54.2108	$54.21	$54.20	$54.20
Purchase #6	$64.72	9.597%	$70.9312	$70.93	$70.95	$70.90
Purchase #7	$59.61	13.807%	$67.8404	$67.84	$67.85	$67.80
7 purchase totals =	$560.80		$612.1748	$612.18	$612.20	$612.00