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	$33.89	11.871%	$37.9131	$37.91	$37.90	$37.90
Purchase #2	$30.78	9.178%	$33.605	$33.61	$33.60	$33.60
Purchase #3	$239.87	13.852%	$273.0968	$273.10	$273.10	$273.10
Purchase #4	$74.78	11.615%	$83.4657	$83.47	$83.45	$83.50
Purchase #5	$245.64	4.525%	$256.7552	$256.76	$256.75	$256.80
Purchase #6	$175.39	3.817%	$182.0846	$182.08	$182.10	$182.10
Purchase #7	$36.96	6.539%	$39.3768	$39.38	$39.40	$39.40
7 purchase totals =	$837.31		$906.2972	$906.31	$906.30	$906.40