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	$139.37	12.229%	$156.4136	$156.41	$156.40	$156.40
Purchase #2	$120.67	3.163%	$124.4868	$124.49	$124.50	$124.50
Purchase #3	$134.85	3.586%	$139.6857	$139.69	$139.70	$139.70
Purchase #4	$226.62	12.478%	$254.8976	$254.90	$254.90	$254.90
Purchase #5	$60.55	12.102%	$67.8778	$67.88	$67.90	$67.90
Purchase #6	$136.30	8.539%	$147.9387	$147.94	$147.95	$147.90
Purchase #7	$100.41	8.729%	$109.1748	$109.17	$109.15	$109.20
7 purchase totals =	$918.77		$1,000.4750	$1,000.48	$1,000.50	$1,000.50