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	$78.56	13.874%	$89.4594	$89.46	$89.45	$89.50
Purchase #2	$29.30	10.566%	$32.3958	$32.40	$32.40	$32.40
Purchase #3	$84.45	6.510%	$89.9477	$89.95	$89.95	$89.90
Purchase #4	$118.70	11.378%	$132.2057	$132.21	$132.20	$132.20
Purchase #5	$69.73	11.736%	$77.9135	$77.91	$77.90	$77.90
Purchase #6	$126.41	8.474%	$137.122	$137.12	$137.10	$137.10
Purchase #7	$82.92	7.226%	$88.9118	$88.91	$88.90	$88.90
7 purchase totals =	$590.07		$647.9559	$647.96	$647.90	$647.90