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	$128.56	8.813%	$139.89	$139.89	$139.90	$139.90
Purchase #2	$50.44	7.558%	$54.2523	$54.25	$54.25	$54.30
Purchase #3	$211.96	12.536%	$238.5313	$238.53	$238.55	$238.50
Purchase #4	$225.49	10.181%	$248.4471	$248.45	$248.45	$248.40
Purchase #5	$226.74	8.387%	$245.7567	$245.76	$245.75	$245.80
Purchase #6	$55.39	13.637%	$62.9435	$62.94	$62.95	$62.90
Purchase #7	$98.30	5.631%	$103.8353	$103.84	$103.85	$103.80
7 purchase totals =	$996.88		$1,093.6562	$1,093.66	$1,093.70	$1,093.60