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	$187.58	12.555%	$211.1307	$211.13	$211.15	$211.10
Purchase #2	$131.30	12.611%	$147.8582	$147.86	$147.85	$147.90
Purchase #3	$76.87	9.165%	$83.9151	$83.92	$83.90	$83.90
Purchase #4	$217.49	8.429%	$235.8222	$235.82	$235.80	$235.80
Purchase #5	$40.59	6.712%	$43.3144	$43.31	$43.30	$43.30
Purchase #6	$41.79	9.290%	$45.6723	$45.67	$45.65	$45.70
Purchase #7	$111.29	11.298%	$123.8635	$123.86	$123.85	$123.90
7 purchase totals =	$806.91		$891.5764	$891.57	$891.50	$891.60