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	$34.40	8.340%	$37.269	$37.27	$37.25	$37.30
Purchase #2	$29.37	9.404%	$32.132	$32.13	$32.15	$32.10
Purchase #3	$248.38	6.570%	$264.6986	$264.70	$264.70	$264.70
Purchase #4	$151.36	9.607%	$165.9012	$165.90	$165.90	$165.90
Purchase #5	$61.67	5.124%	$64.83	$64.83	$64.85	$64.80
Purchase #6	$186.59	9.557%	$204.4224	$204.42	$204.40	$204.40
Purchase #7	$37.79	7.443%	$40.6027	$40.60	$40.60	$40.60
7 purchase totals =	$749.56		$809.8559	$809.85	$809.85	$809.80