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	$65.89	9.405%	$72.087	$72.09	$72.10	$72.10
Purchase #2	$84.96	6.132%	$90.1697	$90.17	$90.15	$90.20
Purchase #3	$236.37	4.332%	$246.6095	$246.61	$246.60	$246.60
Purchase #4	$92.44	6.256%	$98.223	$98.22	$98.20	$98.20
Purchase #5	$31.46	5.716%	$33.2583	$33.26	$33.25	$33.30
Purchase #6	$83.32	10.209%	$91.8261	$91.83	$91.85	$91.80
Purchase #7	$32.39	3.302%	$33.4595	$33.46	$33.45	$33.50
7 purchase totals =	$626.83		$665.6331	$665.64	$665.60	$665.70