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	$83.46	6.159%	$88.6003	$88.60	$88.60	$88.60
Purchase #2	$182.32	13.270%	$206.5139	$206.51	$206.50	$206.50
Purchase #3	$223.69	13.266%	$253.3647	$253.36	$253.35	$253.40
Purchase #4	$244.57	7.459%	$262.8125	$262.81	$262.80	$262.80
Purchase #5	$16.52	11.136%	$18.3597	$18.36	$18.35	$18.40
Purchase #6	$79.94	11.364%	$89.0244	$89.02	$89.00	$89.00
Purchase #7	$33.44	9.196%	$36.5151	$36.52	$36.50	$36.50
7 purchase totals =	$863.94		$955.1906	$955.18	$955.10	$955.20