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	$123.84	12.513%	$139.3361	$139.34	$139.35	$139.30
Purchase #2	$61.94	4.669%	$64.832	$64.83	$64.85	$64.80
Purchase #3	$31.55	8.629%	$34.2724	$34.27	$34.25	$34.30
Purchase #4	$125.79	4.715%	$131.721	$131.72	$131.70	$131.70
Purchase #5	$191.64	4.674%	$200.5973	$200.60	$200.60	$200.60
Purchase #6	$151.78	4.588%	$158.7437	$158.74	$158.75	$158.70
Purchase #7	$107.33	8.404%	$116.35	$116.35	$116.35	$116.40
7 purchase totals =	$793.87		$845.8525	$845.85	$845.85	$845.80