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	$37.97	11.416%	$42.3047	$42.30	$42.30	$42.30
Purchase #2	$182.89	12.425%	$205.6141	$205.61	$205.60	$205.60
Purchase #3	$246.39	11.501%	$274.7273	$274.73	$274.75	$274.70
Purchase #4	$209.59	6.170%	$222.5217	$222.52	$222.50	$222.50
Purchase #5	$79.42	12.550%	$89.3872	$89.39	$89.40	$89.40
Purchase #6	$77.76	8.218%	$84.1503	$84.15	$84.15	$84.20
Purchase #7	$152.84	9.352%	$167.1336	$167.13	$167.15	$167.10
7 purchase totals =	$986.86		$1,085.8389	$1,085.83	$1,085.85	$1,085.80