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	$127.36	9.263%	$139.1574	$139.16	$139.15	$139.20
Purchase #2	$248.39	10.720%	$275.0174	$275.02	$275.00	$275.00
Purchase #3	$52.54	12.837%	$59.2846	$59.28	$59.30	$59.30
Purchase #4	$100.29	12.698%	$113.0248	$113.02	$113.00	$113.00
Purchase #5	$42.28	11.231%	$47.0285	$47.03	$47.05	$47.00
Purchase #6	$34.45	8.744%	$37.4623	$37.46	$37.45	$37.50
Purchase #7	$73.37	11.839%	$82.0563	$82.06	$82.05	$82.10
7 purchase totals =	$678.68		$753.0313	$753.03	$753.00	$753.10