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	$208.83	5.151%	$219.5868	$219.59	$219.60	$219.60
Purchase #2	$142.59	9.666%	$156.3727	$156.37	$156.35	$156.40
Purchase #3	$36.53	6.377%	$38.8595	$38.86	$38.85	$38.90
Purchase #4	$190.46	10.118%	$209.7307	$209.73	$209.75	$209.70
Purchase #5	$74.57	10.253%	$82.2157	$82.22	$82.20	$82.20
Purchase #6	$81.56	13.184%	$92.3129	$92.31	$92.30	$92.30
Purchase #7	$46.97	7.536%	$50.5097	$50.51	$50.50	$50.50
7 purchase totals =	$781.51		$849.5880	$849.59	$849.55	$849.60