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	$146.51	12.206%	$164.393	$164.39	$164.40	$164.40
Purchase #2	$180.78	4.802%	$189.4611	$189.46	$189.45	$189.50
Purchase #3	$99.85	9.735%	$109.5704	$109.57	$109.55	$109.60
Purchase #4	$83.79	5.763%	$88.6188	$88.62	$88.60	$88.60
Purchase #5	$249.37	13.713%	$283.5661	$283.57	$283.55	$283.60
Purchase #6	$193.29	13.775%	$219.9157	$219.92	$219.90	$219.90
Purchase #7	$32.60	9.318%	$35.6377	$35.64	$35.65	$35.60
7 purchase totals =	$986.19		$1,091.1628	$1,091.17	$1,091.10	$1,091.20