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	$84.30	6.840%	$90.0661	$90.07	$90.05	$90.10
Purchase #2	$133.37	5.527%	$140.7414	$140.74	$140.75	$140.70
Purchase #3	$26.72	6.322%	$28.4092	$28.41	$28.40	$28.40
Purchase #4	$248.94	8.704%	$270.6077	$270.61	$270.60	$270.60
Purchase #5	$62.89	13.223%	$71.2059	$71.21	$71.20	$71.20
Purchase #6	$192.34	13.656%	$218.606	$218.61	$218.60	$218.60
Purchase #7	$84.88	6.574%	$90.46	$90.46	$90.45	$90.50
7 purchase totals =	$833.44		$910.0963	$910.11	$910.05	$910.10