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	$79.42	12.521%	$89.3642	$89.36	$89.35	$89.40
Purchase #2	$51.65	6.648%	$55.0837	$55.08	$55.10	$55.10
Purchase #3	$122.77	4.204%	$127.9313	$127.93	$127.95	$127.90
Purchase #4	$49.71	5.243%	$52.3163	$52.32	$52.30	$52.30
Purchase #5	$9.33	6.220%	$9.9103	$9.91	$9.90	$9.90
Purchase #6	$210.83	11.614%	$235.3158	$235.32	$235.30	$235.30
Purchase #7	$117.33	12.373%	$131.8472	$131.85	$131.85	$131.80
7 purchase totals =	$641.04		$701.7688	$701.77	$701.75	$701.70