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	$97.78	5.870%	$103.5197	$103.52	$103.50	$103.50
Purchase #2	$243.89	7.662%	$262.5769	$262.58	$262.60	$262.60
Purchase #3	$223.62	7.359%	$240.0762	$240.08	$240.10	$240.10
Purchase #4	$101.68	12.365%	$114.2527	$114.25	$114.25	$114.30
Purchase #5	$126.39	4.289%	$131.8109	$131.81	$131.80	$131.80
Purchase #6	$115.88	3.774%	$120.2533	$120.25	$120.25	$120.30
Purchase #7	$167.86	4.423%	$175.2844	$175.28	$175.30	$175.30
7 purchase totals =	$1,077.10		$1,147.7741	$1,147.77	$1,147.80	$1,147.90