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	$100.50	12.852%	$113.4163	$113.42	$113.40	$113.40
Purchase #2	$134.34	3.499%	$139.0406	$139.04	$139.05	$139.00
Purchase #3	$40.48	11.113%	$44.9785	$44.98	$45.00	$45.00
Purchase #4	$65.35	10.803%	$72.4098	$72.41	$72.40	$72.40
Purchase #5	$150.61	13.258%	$170.5779	$170.58	$170.60	$170.60
Purchase #6	$142.75	3.460%	$147.6892	$147.69	$147.70	$147.70
Purchase #7	$174.83	9.631%	$191.6679	$191.67	$191.65	$191.70
7 purchase totals =	$808.86		$879.7802	$879.79	$879.80	$879.80