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	$241.37	12.818%	$272.3088	$272.31	$272.30	$272.30
Purchase #2	$82.60	8.240%	$89.4062	$89.41	$89.40	$89.40
Purchase #3	$74.72	6.860%	$79.8458	$79.85	$79.85	$79.80
Purchase #4	$166.97	13.821%	$190.0469	$190.05	$190.05	$190.00
Purchase #5	$155.50	10.527%	$171.8695	$171.87	$171.85	$171.90
Purchase #6	$188.88	12.629%	$212.7337	$212.73	$212.75	$212.70
Purchase #7	$75.96	12.702%	$85.6084	$85.61	$85.60	$85.60
7 purchase totals =	$986.00		$1,101.8193	$1,101.83	$1,101.80	$1,101.70