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	$54.86	4.253%	$57.1932	$57.19	$57.20	$57.20
Purchase #2	$250.48	4.640%	$262.1023	$262.10	$262.10	$262.10
Purchase #3	$238.33	8.816%	$259.3412	$259.34	$259.35	$259.30
Purchase #4	$249.90	5.372%	$263.3246	$263.32	$263.30	$263.30
Purchase #5	$151.59	13.756%	$172.4427	$172.44	$172.45	$172.40
Purchase #6	$166.48	10.476%	$183.9204	$183.92	$183.90	$183.90
Purchase #7	$96.46	6.173%	$102.4145	$102.41	$102.40	$102.40
7 purchase totals =	$1,208.10		$1,300.7389	$1,300.72	$1,300.70	$1,300.60