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	$46.88	13.179%	$53.0583	$53.06	$53.05	$53.10
Purchase #2	$135.84	6.232%	$144.3055	$144.31	$144.30	$144.30
Purchase #3	$248.65	12.127%	$278.8038	$278.80	$278.80	$278.80
Purchase #4	$54.70	12.347%	$61.4538	$61.45	$61.45	$61.50
Purchase #5	$83.85	9.703%	$91.986	$91.99	$92.00	$92.00
Purchase #6	$168.44	11.268%	$187.4198	$187.42	$187.40	$187.40
Purchase #7	$240.39	13.736%	$273.41	$273.41	$273.40	$273.40
7 purchase totals =	$978.75		$1,090.4372	$1,090.44	$1,090.40	$1,090.50