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	$83.86	7.195%	$89.8937	$89.89	$89.90	$89.90
Purchase #2	$145.74	10.444%	$160.9611	$160.96	$160.95	$161.00
Purchase #3	$104.51	7.454%	$112.3002	$112.30	$112.30	$112.30
Purchase #4	$148.28	9.242%	$161.984	$161.98	$162.00	$162.00
Purchase #5	$224.94	5.272%	$236.7988	$236.80	$236.80	$236.80
Purchase #6	$59.25	4.189%	$61.732	$61.73	$61.75	$61.70
Purchase #7	$72.81	7.813%	$78.4986	$78.50	$78.50	$78.50
7 purchase totals =	$839.39		$902.1684	$902.16	$902.20	$902.20