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	$233.37	13.363%	$264.5552	$264.56	$264.55	$264.60
Purchase #2	$47.91	5.149%	$50.3769	$50.38	$50.40	$50.40
Purchase #3	$150.96	11.439%	$168.2283	$168.23	$168.25	$168.20
Purchase #4	$75.66	12.261%	$84.9367	$84.94	$84.95	$84.90
Purchase #5	$118.89	8.242%	$128.6889	$128.69	$128.70	$128.70
Purchase #6	$236.57	7.744%	$254.89	$254.89	$254.90	$254.90
Purchase #7	$138.50	4.407%	$144.6037	$144.60	$144.60	$144.60
7 purchase totals =	$1,001.86		$1,096.2797	$1,096.29	$1,096.35	$1,096.30