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	$53.31	11.668%	$59.5302	$59.53	$59.55	$59.50
Purchase #2	$86.87	13.871%	$98.9197	$98.92	$98.90	$98.90
Purchase #3	$226.74	12.133%	$254.2504	$254.25	$254.25	$254.30
Purchase #4	$154.63	11.782%	$172.8485	$172.85	$172.85	$172.80
Purchase #5	$183.73	11.696%	$205.2191	$205.22	$205.20	$205.20
Purchase #6	$146.88	11.661%	$164.0077	$164.01	$164.00	$164.00
Purchase #7	$68.59	10.837%	$76.0231	$76.02	$76.00	$76.00
7 purchase totals =	$920.75		$1,030.7987	$1,030.80	$1,030.75	$1,030.70