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	$85.26	12.402%	$95.8339	$95.83	$95.85	$95.80
Purchase #2	$105.51	6.454%	$112.3196	$112.32	$112.30	$112.30
Purchase #3	$63.27	7.649%	$68.1095	$68.11	$68.10	$68.10
Purchase #4	$7.92	8.814%	$8.6181	$8.62	$8.60	$8.60
Purchase #5	$102.70	8.680%	$111.6144	$111.61	$111.60	$111.60
Purchase #6	$240.51	11.786%	$268.8565	$268.86	$268.85	$268.90
Purchase #7	$100.33	8.532%	$108.8902	$108.89	$108.90	$108.90
7 purchase totals =	$705.50		$774.2422	$774.24	$774.20	$774.20