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	$69.84	12.464%	$78.5449	$78.54	$78.55	$78.50
Purchase #2	$81.30	12.637%	$91.5739	$91.57	$91.55	$91.60
Purchase #3	$87.60	5.574%	$92.4828	$92.48	$92.50	$92.50
Purchase #4	$248.33	8.351%	$269.068	$269.07	$269.05	$269.10
Purchase #5	$211.32	9.490%	$231.3743	$231.37	$231.35	$231.40
Purchase #6	$13.74	7.421%	$14.7596	$14.76	$14.75	$14.80
Purchase #7	$95.67	8.277%	$103.5886	$103.59	$103.60	$103.60
7 purchase totals =	$807.80		$881.3921	$881.38	$881.35	$881.50