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	$247.51	6.406%	$263.3655	$263.37	$263.35	$263.40
Purchase #2	$147.44	11.646%	$164.6109	$164.61	$164.60	$164.60
Purchase #3	$18.48	12.663%	$20.8201	$20.82	$20.80	$20.80
Purchase #4	$87.96	11.558%	$98.1264	$98.13	$98.15	$98.10
Purchase #5	$135.60	6.645%	$144.6106	$144.61	$144.60	$144.60
Purchase #6	$20.54	4.486%	$21.4614	$21.46	$21.45	$21.50
Purchase #7	$6.54	8.250%	$7.0796	$7.08	$7.10	$7.10
7 purchase totals =	$664.07		$720.0745	$720.08	$720.05	$720.10