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	$164.71	12.828%	$185.839	$185.84	$185.85	$185.80
Purchase #2	$99.58	7.256%	$106.8055	$106.81	$106.80	$106.80
Purchase #3	$128.83	11.268%	$143.3466	$143.35	$143.35	$143.30
Purchase #4	$78.92	6.380%	$83.9551	$83.96	$83.95	$84.00
Purchase #5	$142.26	9.120%	$155.2341	$155.23	$155.25	$155.20
Purchase #6	$53.43	3.139%	$55.1072	$55.11	$55.10	$55.10
Purchase #7	$243.64	7.738%	$262.4929	$262.49	$262.50	$262.50
7 purchase totals =	$911.37		$992.7804	$992.79	$992.80	$992.70