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	$63.56	9.168%	$69.3872	$69.39	$69.40	$69.40
Purchase #2	$179.71	11.566%	$200.4953	$200.50	$200.50	$200.50
Purchase #3	$92.36	11.844%	$103.2991	$103.30	$103.30	$103.30
Purchase #4	$203.88	3.743%	$211.5112	$211.51	$211.50	$211.50
Purchase #5	$156.27	7.580%	$168.1153	$168.12	$168.10	$168.10
Purchase #6	$17.55	11.642%	$19.5932	$19.59	$19.60	$19.60
Purchase #7	$86.32	5.724%	$91.261	$91.26	$91.25	$91.30
7 purchase totals =	$799.65		$863.6623	$863.67	$863.65	$863.70