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	$76.78	6.280%	$81.6018	$81.60	$81.60	$81.60
Purchase #2	$250.47	10.561%	$276.9221	$276.92	$276.90	$276.90
Purchase #3	$18.86	7.395%	$20.2547	$20.25	$20.25	$20.30
Purchase #4	$94.86	10.780%	$105.0859	$105.09	$105.10	$105.10
Purchase #5	$55.65	7.664%	$59.915	$59.92	$59.90	$59.90
Purchase #6	$110.78	13.538%	$125.7774	$125.78	$125.80	$125.80
Purchase #7	$85.64	12.379%	$96.2414	$96.24	$96.25	$96.20
7 purchase totals =	$693.04		$765.7983	$765.80	$765.80	$765.80