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	$96.46	3.855%	$100.1785	$100.18	$100.20	$100.20
Purchase #2	$141.81	10.390%	$156.5441	$156.54	$156.55	$156.50
Purchase #3	$33.93	9.198%	$37.0509	$37.05	$37.05	$37.10
Purchase #4	$49.42	5.859%	$52.3155	$52.32	$52.30	$52.30
Purchase #5	$245.36	12.260%	$275.4411	$275.44	$275.45	$275.40
Purchase #6	$141.60	4.648%	$148.1816	$148.18	$148.20	$148.20
Purchase #7	$239.84	12.141%	$268.959	$268.96	$268.95	$269.00
7 purchase totals =	$948.42		$1,038.6707	$1,038.67	$1,038.70	$1,038.70