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	$119.73	10.171%	$131.9077	$131.91	$131.90	$131.90
Purchase #2	$99.55	10.425%	$109.9281	$109.93	$109.95	$109.90
Purchase #3	$141.49	5.378%	$149.0993	$149.10	$149.10	$149.10
Purchase #4	$114.83	8.320%	$124.3839	$124.38	$124.40	$124.40
Purchase #5	$144.45	7.659%	$155.5134	$155.51	$155.50	$155.50
Purchase #6	$205.87	13.324%	$233.3001	$233.30	$233.30	$233.30
Purchase #7	$32.43	9.467%	$35.5001	$35.50	$35.50	$35.50
7 purchase totals =	$858.35		$939.6326	$939.63	$939.65	$939.60