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	$25.41	9.684%	$27.8707	$27.87	$27.85	$27.90
Purchase #2	$63.91	13.362%	$72.4497	$72.45	$72.45	$72.40
Purchase #3	$29.92	5.621%	$31.6018	$31.60	$31.60	$31.60
Purchase #4	$214.47	10.464%	$236.9121	$236.91	$236.90	$236.90
Purchase #5	$248.55	10.201%	$273.9046	$273.90	$273.90	$273.90
Purchase #6	$51.89	11.445%	$57.8288	$57.83	$57.85	$57.80
Purchase #7	$91.73	3.868%	$95.2781	$95.28	$95.30	$95.30
7 purchase totals =	$725.88		$795.8458	$795.84	$795.85	$795.80