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	$76.87	11.280%	$85.5409	$85.54	$85.55	$85.50
Purchase #2	$85.37	7.508%	$91.7796	$91.78	$91.80	$91.80
Purchase #3	$134.54	6.750%	$143.6215	$143.62	$143.60	$143.60
Purchase #4	$233.90	3.569%	$242.2479	$242.25	$242.25	$242.20
Purchase #5	$107.59	11.705%	$120.1834	$120.18	$120.20	$120.20
Purchase #6	$59.44	9.136%	$64.8704	$64.87	$64.85	$64.90
Purchase #7	$86.64	6.443%	$92.2222	$92.22	$92.20	$92.20
7 purchase totals =	$784.35		$840.4659	$840.46	$840.45	$840.40