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	$220.73	13.317%	$250.1246	$250.12	$250.10	$250.10
Purchase #2	$139.38	9.170%	$152.1611	$152.16	$152.15	$152.20
Purchase #3	$194.76	9.826%	$213.8971	$213.90	$213.90	$213.90
Purchase #4	$93.47	6.471%	$99.5184	$99.52	$99.50	$99.50
Purchase #5	$188.26	8.394%	$204.0625	$204.06	$204.05	$204.10
Purchase #6	$69.39	4.225%	$72.3217	$72.32	$72.30	$72.30
Purchase #7	$19.50	9.615%	$21.3749	$21.37	$21.35	$21.40
7 purchase totals =	$925.49		$1,013.4603	$1,013.45	$1,013.35	$1,013.50