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	$178.54	11.410%	$198.9114	$198.91	$198.90	$198.90
Purchase #2	$27.43	13.497%	$31.1322	$31.13	$31.15	$31.10
Purchase #3	$76.49	9.639%	$83.8629	$83.86	$83.85	$83.90
Purchase #4	$132.75	7.452%	$142.6425	$142.64	$142.65	$142.60
Purchase #5	$13.62	7.446%	$14.6341	$14.63	$14.65	$14.60
Purchase #6	$95.88	3.670%	$99.3988	$99.40	$99.40	$99.40
Purchase #7	$103.35	7.291%	$110.8852	$110.89	$110.90	$110.90
7 purchase totals =	$628.06		$681.4671	$681.46	$681.50	$681.40