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	$245.35	13.198%	$277.7313	$277.73	$277.75	$277.70
Purchase #2	$217.37	10.808%	$240.8633	$240.86	$240.85	$240.90
Purchase #3	$73.48	12.793%	$82.8803	$82.88	$82.90	$82.90
Purchase #4	$118.87	10.531%	$131.3882	$131.39	$131.40	$131.40
Purchase #5	$12.32	7.753%	$13.2752	$13.28	$13.30	$13.30
Purchase #6	$25.38	3.710%	$26.3216	$26.32	$26.30	$26.30
Purchase #7	$70.97	10.423%	$78.3672	$78.37	$78.35	$78.40
7 purchase totals =	$763.74		$850.8271	$850.83	$850.85	$850.90