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	$104.28	4.614%	$109.0915	$109.09	$109.10	$109.10
Purchase #2	$131.91	4.860%	$138.3208	$138.32	$138.30	$138.30
Purchase #3	$247.52	8.330%	$268.1384	$268.14	$268.15	$268.10
Purchase #4	$28.63	13.842%	$32.593	$32.59	$32.60	$32.60
Purchase #5	$196.91	6.235%	$209.1873	$209.19	$209.20	$209.20
Purchase #6	$248.72	5.219%	$261.7007	$261.70	$261.70	$261.70
Purchase #7	$142.85	7.732%	$153.8952	$153.90	$153.90	$153.90
7 purchase totals =	$1,100.82		$1,172.9269	$1,172.93	$1,172.95	$1,172.90