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	$22.39	7.715%	$24.1174	$24.12	$24.10	$24.10
Purchase #2	$167.92	12.799%	$189.4121	$189.41	$189.40	$189.40
Purchase #3	$144.46	8.371%	$156.5527	$156.55	$156.55	$156.60
Purchase #4	$65.91	12.625%	$74.2311	$74.23	$74.25	$74.20
Purchase #5	$118.33	11.128%	$131.4978	$131.50	$131.50	$131.50
Purchase #6	$126.35	11.413%	$140.7703	$140.77	$140.75	$140.80
Purchase #7	$95.47	4.711%	$99.9676	$99.97	$99.95	$100.00
7 purchase totals =	$740.83		$816.5490	$816.55	$816.50	$816.60