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	$40.50	8.339%	$43.8773	$43.88	$43.90	$43.90
Purchase #2	$165.90	7.478%	$178.306	$178.31	$178.30	$178.30
Purchase #3	$41.95	11.191%	$46.6446	$46.64	$46.65	$46.60
Purchase #4	$96.89	13.380%	$109.8539	$109.85	$109.85	$109.90
Purchase #5	$200.68	4.597%	$209.9053	$209.91	$209.90	$209.90
Purchase #6	$36.46	12.321%	$40.9522	$40.95	$40.95	$41.00
Purchase #7	$120.45	7.340%	$129.291	$129.29	$129.30	$129.30
7 purchase totals =	$702.83		$758.8303	$758.83	$758.85	$758.90