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	$91.72	9.838%	$100.7434	$100.74	$100.75	$100.70
Purchase #2	$244.52	7.177%	$262.0692	$262.07	$262.05	$262.10
Purchase #3	$64.96	11.681%	$72.548	$72.55	$72.55	$72.50
Purchase #4	$134.93	3.459%	$139.5972	$139.60	$139.60	$139.60
Purchase #5	$27.34	12.790%	$30.8368	$30.84	$30.85	$30.80
Purchase #6	$166.89	7.166%	$178.8493	$178.85	$178.85	$178.80
Purchase #7	$46.44	11.674%	$51.8614	$51.86	$51.85	$51.90
7 purchase totals =	$776.80		$836.5053	$836.51	$836.50	$836.40