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	$72.87	12.177%	$81.7434	$81.74	$81.75	$81.70
Purchase #2	$135.26	8.576%	$146.8599	$146.86	$146.85	$146.90
Purchase #3	$171.93	6.284%	$182.7341	$182.73	$182.75	$182.70
Purchase #4	$241.43	11.640%	$269.5325	$269.53	$269.55	$269.50
Purchase #5	$55.97	6.797%	$59.7743	$59.77	$59.75	$59.80
Purchase #6	$46.29	7.126%	$49.5886	$49.59	$49.60	$49.60
Purchase #7	$245.83	4.406%	$256.6613	$256.66	$256.65	$256.70
7 purchase totals =	$969.58		$1,046.8941	$1,046.88	$1,046.90	$1,046.90