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	$234.61	8.212%	$253.8762	$253.88	$253.90	$253.90
Purchase #2	$90.42	8.847%	$98.4195	$98.42	$98.40	$98.40
Purchase #3	$176.83	5.634%	$186.7926	$186.79	$186.80	$186.80
Purchase #4	$105.51	3.677%	$109.3896	$109.39	$109.40	$109.40
Purchase #5	$88.33	6.341%	$93.931	$93.93	$93.95	$93.90
Purchase #6	$58.49	4.838%	$61.3197	$61.32	$61.30	$61.30
Purchase #7	$162.33	3.117%	$167.3898	$167.39	$167.40	$167.40
7 purchase totals =	$916.52		$971.1184	$971.12	$971.15	$971.10