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	$188.81	10.857%	$209.3091	$209.31	$209.30	$209.30
Purchase #2	$139.73	10.189%	$153.9671	$153.97	$153.95	$154.00
Purchase #3	$150.56	12.789%	$169.8151	$169.82	$169.80	$169.80
Purchase #4	$70.32	11.358%	$78.3069	$78.31	$78.30	$78.30
Purchase #5	$147.43	11.258%	$164.0277	$164.03	$164.05	$164.00
Purchase #6	$238.70	12.469%	$268.4635	$268.46	$268.45	$268.50
Purchase #7	$153.30	4.518%	$160.2261	$160.23	$160.25	$160.20
7 purchase totals =	$1,088.85		$1,204.1155	$1,204.13	$1,204.10	$1,204.10