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	$233.29	6.523%	$248.5075	$248.51	$248.50	$248.50
Purchase #2	$182.62	4.769%	$191.3291	$191.33	$191.35	$191.30
Purchase #3	$230.88	11.870%	$258.2855	$258.29	$258.30	$258.30
Purchase #4	$96.61	11.647%	$107.8622	$107.86	$107.85	$107.90
Purchase #5	$18.86	7.865%	$20.3433	$20.34	$20.35	$20.30
Purchase #6	$20.89	4.454%	$21.8204	$21.82	$21.80	$21.80
Purchase #7	$215.57	11.547%	$240.4619	$240.46	$240.45	$240.50
7 purchase totals =	$998.72		$1,088.6099	$1,088.61	$1,088.60	$1,088.60