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	$169.90	4.112%	$176.8863	$176.89	$176.90	$176.90
Purchase #2	$223.29	5.865%	$236.386	$236.39	$236.40	$236.40
Purchase #3	$85.51	7.379%	$91.8198	$91.82	$91.80	$91.80
Purchase #4	$33.33	11.684%	$37.2243	$37.22	$37.20	$37.20
Purchase #5	$214.88	10.785%	$238.0548	$238.05	$238.05	$238.10
Purchase #6	$250.60	8.324%	$271.4599	$271.46	$271.45	$271.50
Purchase #7	$25.67	9.626%	$28.141	$28.14	$28.15	$28.10
7 purchase totals =	$1,003.18		$1,079.9721	$1,079.97	$1,079.95	$1,080.00