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	$5.33	12.417%	$5.9918	$5.99	$6.00	$6.00
Purchase #2	$41.64	12.365%	$46.7888	$46.79	$46.80	$46.80
Purchase #3	$18.92	8.841%	$20.5927	$20.59	$20.60	$20.60
Purchase #4	$162.40	3.644%	$168.3179	$168.32	$168.30	$168.30
Purchase #5	$145.82	3.156%	$150.4221	$150.42	$150.40	$150.40
Purchase #6	$109.57	4.596%	$114.6058	$114.61	$114.60	$114.60
Purchase #7	$164.92	13.143%	$186.5954	$186.60	$186.60	$186.60
7 purchase totals =	$648.60		$693.3145	$693.32	$693.30	$693.30