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	$73.97	6.397%	$78.7019	$78.70	$78.70	$78.70
Purchase #2	$86.57	3.182%	$89.3247	$89.32	$89.30	$89.30
Purchase #3	$100.66	13.667%	$114.4172	$114.42	$114.40	$114.40
Purchase #4	$133.25	3.359%	$137.7259	$137.73	$137.75	$137.70
Purchase #5	$85.84	13.255%	$97.2181	$97.22	$97.20	$97.20
Purchase #6	$171.77	8.157%	$185.7813	$185.78	$185.80	$185.80
Purchase #7	$76.26	6.458%	$81.1849	$81.18	$81.20	$81.20
7 purchase totals =	$728.32		$784.3540	$784.35	$784.35	$784.30