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	$141.32	10.475%	$156.1233	$156.12	$156.10	$156.10
Purchase #2	$90.52	4.430%	$94.53	$94.53	$94.55	$94.50
Purchase #3	$5.82	12.156%	$6.5275	$6.53	$6.55	$6.50
Purchase #4	$72.83	10.532%	$80.5005	$80.50	$80.50	$80.50
Purchase #5	$52.29	6.308%	$55.5885	$55.59	$55.60	$55.60
Purchase #6	$182.99	4.420%	$191.0782	$191.08	$191.10	$191.10
Purchase #7	$28.85	11.498%	$32.1672	$32.17	$32.15	$32.20
7 purchase totals =	$574.62		$616.5152	$616.52	$616.55	$616.50