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	$70.43	10.587%	$77.8864	$77.89	$77.90	$77.90
Purchase #2	$186.61	13.611%	$212.0095	$212.01	$212.00	$212.00
Purchase #3	$29.36	13.441%	$33.3063	$33.31	$33.30	$33.30
Purchase #4	$49.66	13.679%	$56.453	$56.45	$56.45	$56.50
Purchase #5	$146.43	6.360%	$155.7429	$155.74	$155.75	$155.70
Purchase #6	$33.85	13.687%	$38.483	$38.48	$38.50	$38.50
Purchase #7	$33.39	4.765%	$34.981	$34.98	$35.00	$35.00
7 purchase totals =	$549.73		$608.8621	$608.86	$608.90	$608.90