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	$203.87	5.204%	$214.4794	$214.48	$214.50	$214.50
Purchase #2	$241.39	13.502%	$273.9825	$273.98	$274.00	$274.00
Purchase #3	$233.68	4.122%	$243.3123	$243.31	$243.30	$243.30
Purchase #4	$97.27	12.617%	$109.5426	$109.54	$109.55	$109.50
Purchase #5	$94.72	3.728%	$98.2512	$98.25	$98.25	$98.30
Purchase #6	$90.72	9.824%	$99.6323	$99.63	$99.65	$99.60
Purchase #7	$218.72	5.799%	$231.4036	$231.40	$231.40	$231.40
7 purchase totals =	$1,180.37		$1,270.6039	$1,270.59	$1,270.65	$1,270.60