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	$85.73	5.243%	$90.2248	$90.22	$90.20	$90.20
Purchase #2	$30.77	4.289%	$32.0897	$32.09	$32.10	$32.10
Purchase #3	$101.32	11.560%	$113.0326	$113.03	$113.05	$113.00
Purchase #4	$99.47	3.198%	$102.6511	$102.65	$102.65	$102.70
Purchase #5	$230.44	8.190%	$249.313	$249.31	$249.30	$249.30
Purchase #6	$195.89	6.713%	$209.0401	$209.04	$209.05	$209.00
Purchase #7	$147.27	7.496%	$158.3094	$158.31	$158.30	$158.30
7 purchase totals =	$890.89		$954.6607	$954.65	$954.65	$954.60