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	$193.54	5.674%	$204.5215	$204.52	$204.50	$204.50
Purchase #2	$92.27	6.236%	$98.024	$98.02	$98.00	$98.00
Purchase #3	$42.53	12.572%	$47.8769	$47.88	$47.90	$47.90
Purchase #4	$83.95	11.855%	$93.9023	$93.90	$93.90	$93.90
Purchase #5	$94.28	9.336%	$103.082	$103.08	$103.10	$103.10
Purchase #6	$47.37	12.667%	$53.3704	$53.37	$53.35	$53.40
Purchase #7	$68.96	13.290%	$78.1248	$78.12	$78.10	$78.10
7 purchase totals =	$622.90		$678.9019	$678.89	$678.85	$678.90