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	$156.85	4.713%	$164.2423	$164.24	$164.25	$164.20
Purchase #2	$127.63	5.435%	$134.5667	$134.57	$134.55	$134.60
Purchase #3	$165.59	13.564%	$188.0506	$188.05	$188.05	$188.10
Purchase #4	$96.77	12.232%	$108.6069	$108.61	$108.60	$108.60
Purchase #5	$221.30	12.590%	$249.1617	$249.16	$249.15	$249.20
Purchase #6	$178.80	6.175%	$189.8409	$189.84	$189.85	$189.80
Purchase #7	$182.89	7.692%	$196.9579	$196.96	$196.95	$197.00
7 purchase totals =	$1,129.83		$1,231.4270	$1,231.43	$1,231.40	$1,231.50