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	$12.90	7.171%	$13.8251	$13.83	$13.85	$13.80
Purchase #2	$168.45	4.427%	$175.9073	$175.91	$175.90	$175.90
Purchase #3	$6.49	12.620%	$7.309	$7.31	$7.30	$7.30
Purchase #4	$69.47	11.614%	$77.5382	$77.54	$77.55	$77.50
Purchase #5	$177.89	10.427%	$196.4386	$196.44	$196.45	$196.40
Purchase #6	$20.82	9.760%	$22.852	$22.85	$22.85	$22.90
Purchase #7	$126.68	11.399%	$141.1203	$141.12	$141.10	$141.10
7 purchase totals =	$582.70		$634.9905	$635.00	$635.00	$634.90