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	$180.30	4.491%	$188.3973	$188.40	$188.40	$188.40
Purchase #2	$180.96	8.703%	$196.7089	$196.71	$196.70	$196.70
Purchase #3	$250.59	10.359%	$276.5486	$276.55	$276.55	$276.50
Purchase #4	$25.66	6.560%	$27.3433	$27.34	$27.35	$27.30
Purchase #5	$120.46	6.194%	$127.9213	$127.92	$127.90	$127.90
Purchase #6	$237.77	12.729%	$268.0357	$268.04	$268.05	$268.00
Purchase #7	$239.44	6.522%	$255.0563	$255.06	$255.05	$255.10
7 purchase totals =	$1,235.18		$1,340.0114	$1,340.02	$1,340.00	$1,339.90