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	$227.67	6.466%	$242.3911	$242.39	$242.40	$242.40
Purchase #2	$100.87	5.515%	$106.433	$106.43	$106.45	$106.40
Purchase #3	$239.39	5.214%	$251.8718	$251.87	$251.85	$251.90
Purchase #4	$86.66	4.769%	$90.7928	$90.79	$90.80	$90.80
Purchase #5	$114.31	7.670%	$123.0776	$123.08	$123.10	$123.10
Purchase #6	$167.45	12.340%	$188.1133	$188.11	$188.10	$188.10
Purchase #7	$73.80	3.236%	$76.1882	$76.19	$76.20	$76.20
7 purchase totals =	$1,010.15		$1,078.8678	$1,078.86	$1,078.90	$1,078.90