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	$102.54	10.360%	$113.1631	$113.16	$113.15	$113.20
Purchase #2	$73.72	11.368%	$82.1005	$82.10	$82.10	$82.10
Purchase #3	$92.44	10.764%	$102.3902	$102.39	$102.40	$102.40
Purchase #4	$181.72	4.622%	$190.1191	$190.12	$190.10	$190.10
Purchase #5	$76.37	3.404%	$78.9696	$78.97	$78.95	$79.00
Purchase #6	$79.25	7.455%	$85.1581	$85.16	$85.15	$85.20
Purchase #7	$126.52	12.753%	$142.6551	$142.66	$142.65	$142.70
7 purchase totals =	$732.56		$794.5557	$794.56	$794.50	$794.70