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	$175.75	3.510%	$181.9188	$181.92	$181.90	$181.90
Purchase #2	$174.52	11.680%	$194.9039	$194.90	$194.90	$194.90
Purchase #3	$131.71	4.523%	$137.6672	$137.67	$137.65	$137.70
Purchase #4	$245.96	7.665%	$264.8128	$264.81	$264.80	$264.80
Purchase #5	$11.76	11.541%	$13.1172	$13.12	$13.10	$13.10
Purchase #6	$72.30	12.261%	$81.1647	$81.16	$81.15	$81.20
Purchase #7	$171.86	9.567%	$188.3018	$188.30	$188.30	$188.30
7 purchase totals =	$983.86		$1,061.8864	$1,061.88	$1,061.80	$1,061.90