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	$36.73	8.601%	$39.8891	$39.89	$39.90	$39.90
Purchase #2	$241.42	4.815%	$253.0444	$253.04	$253.05	$253.00
Purchase #3	$100.44	9.420%	$109.9014	$109.90	$109.90	$109.90
Purchase #4	$35.59	9.139%	$38.8426	$38.84	$38.85	$38.80
Purchase #5	$166.59	13.216%	$188.6065	$188.61	$188.60	$188.60
Purchase #6	$27.30	4.443%	$28.5129	$28.51	$28.50	$28.50
Purchase #7	$161.28	5.174%	$169.6246	$169.62	$169.60	$169.60
7 purchase totals =	$769.35		$828.4215	$828.41	$828.40	$828.30