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	$80.56	13.340%	$91.3067	$91.31	$91.30	$91.30
Purchase #2	$152.79	6.497%	$162.7168	$162.72	$162.70	$162.70
Purchase #3	$185.53	11.186%	$206.2834	$206.28	$206.30	$206.30
Purchase #4	$238.66	9.723%	$261.8649	$261.86	$261.85	$261.90
Purchase #5	$38.56	10.485%	$42.603	$42.60	$42.60	$42.60
Purchase #6	$97.26	3.159%	$100.3324	$100.33	$100.35	$100.30
Purchase #7	$31.98	3.842%	$33.2087	$33.21	$33.20	$33.20
7 purchase totals =	$825.34		$898.3159	$898.31	$898.30	$898.30