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	$229.85	12.212%	$257.9193	$257.92	$257.90	$257.90
Purchase #2	$176.51	4.591%	$184.6136	$184.61	$184.60	$184.60
Purchase #3	$146.43	11.280%	$162.9473	$162.95	$162.95	$162.90
Purchase #4	$29.53	12.158%	$33.1203	$33.12	$33.10	$33.10
Purchase #5	$54.71	7.111%	$58.6004	$58.60	$58.60	$58.60
Purchase #6	$142.92	4.157%	$148.8612	$148.86	$148.85	$148.90
Purchase #7	$201.77	6.698%	$215.2846	$215.28	$215.30	$215.30
7 purchase totals =	$981.72		$1,061.3467	$1,061.34	$1,061.30	$1,061.30