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	$55.44	4.425%	$57.8932	$57.89	$57.90	$57.90
Purchase #2	$203.47	12.192%	$228.2771	$228.28	$228.30	$228.30
Purchase #3	$218.72	8.494%	$237.2981	$237.30	$237.30	$237.30
Purchase #4	$246.61	5.266%	$259.5965	$259.60	$259.60	$259.60
Purchase #5	$240.99	11.272%	$268.1544	$268.15	$268.15	$268.20
Purchase #6	$83.98	7.653%	$90.407	$90.41	$90.40	$90.40
Purchase #7	$22.35	9.711%	$24.5204	$24.52	$24.50	$24.50
7 purchase totals =	$1,071.56		$1,166.1467	$1,166.15	$1,166.15	$1,166.20