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	$80.79	12.240%	$90.6787	$90.68	$90.70	$90.70
Purchase #2	$75.71	8.582%	$82.2074	$82.21	$82.20	$82.20
Purchase #3	$16.61	9.638%	$18.2109	$18.21	$18.20	$18.20
Purchase #4	$85.60	12.160%	$96.009	$96.01	$96.00	$96.00
Purchase #5	$161.31	6.267%	$171.4193	$171.42	$171.40	$171.40
Purchase #6	$70.38	4.745%	$73.7195	$73.72	$73.70	$73.70
Purchase #7	$212.99	4.428%	$222.4212	$222.42	$222.40	$222.40
7 purchase totals =	$703.39		$754.6660	$754.67	$754.60	$754.60