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	$93.71	9.783%	$102.8776	$102.88	$102.90	$102.90
Purchase #2	$115.41	4.501%	$120.6046	$120.60	$120.60	$120.60
Purchase #3	$205.95	12.435%	$231.5599	$231.56	$231.55	$231.60
Purchase #4	$119.57	7.798%	$128.8941	$128.89	$128.90	$128.90
Purchase #5	$165.46	8.347%	$179.2709	$179.27	$179.25	$179.30
Purchase #6	$48.81	10.336%	$53.855	$53.86	$53.85	$53.90
Purchase #7	$142.46	6.714%	$152.0248	$152.02	$152.00	$152.00
7 purchase totals =	$891.37		$969.0869	$969.08	$969.05	$969.20