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	$202.25	7.860%	$218.1469	$218.15	$218.15	$218.10
Purchase #2	$244.50	6.363%	$260.0575	$260.06	$260.05	$260.10
Purchase #3	$43.75	6.587%	$46.6318	$46.63	$46.65	$46.60
Purchase #4	$35.84	5.657%	$37.8675	$37.87	$37.85	$37.90
Purchase #5	$133.43	4.214%	$139.0527	$139.05	$139.05	$139.10
Purchase #6	$127.47	3.114%	$131.4394	$131.44	$131.45	$131.40
Purchase #7	$92.66	12.740%	$104.4649	$104.46	$104.45	$104.50
7 purchase totals =	$879.90		$937.6607	$937.66	$937.65	$937.70