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	$70.78	13.482%	$80.3226	$80.32	$80.30	$80.30
Purchase #2	$34.30	8.714%	$37.2889	$37.29	$37.30	$37.30
Purchase #3	$165.39	3.597%	$171.3391	$171.34	$171.35	$171.30
Purchase #4	$164.84	11.806%	$184.301	$184.30	$184.30	$184.30
Purchase #5	$28.59	8.585%	$31.0445	$31.04	$31.05	$31.00
Purchase #6	$176.58	10.441%	$195.0167	$195.02	$195.00	$195.00
Purchase #7	$109.39	6.301%	$116.2827	$116.28	$116.30	$116.30
7 purchase totals =	$749.87		$815.5955	$815.59	$815.60	$815.50