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	$56.27	5.618%	$59.4312	$59.43	$59.45	$59.40
Purchase #2	$56.58	5.844%	$59.8865	$59.89	$59.90	$59.90
Purchase #3	$24.90	7.823%	$26.8479	$26.85	$26.85	$26.80
Purchase #4	$220.58	9.334%	$241.1689	$241.17	$241.15	$241.20
Purchase #5	$25.60	12.478%	$28.7944	$28.79	$28.80	$28.80
Purchase #6	$193.31	3.440%	$199.9599	$199.96	$199.95	$200.00
Purchase #7	$146.84	3.450%	$151.906	$151.91	$151.90	$151.90
7 purchase totals =	$724.08		$767.9948	$768.00	$768.00	$768.00